case study and literature review

Organizing Your Social Sciences Research Paper: Writing a Case Study

• Purpose of Guide
• Design Flaws to Avoid
• Independent and Dependent Variables
• Glossary of Research Terms
• Narrowing a Topic Idea
• Broadening a Topic Idea
• Extending the Timeliness of a Topic Idea
• Academic Writing Style
• Choosing a Title
• Making an Outline
• Paragraph Development
• Executive Summary
• The C.A.R.S. Model
• Background Information
• The Research Problem/Question
• Theoretical Framework
• Citation Tracking
• Content Alert Services
• Evaluating Sources
• Reading Research Effectively
• Primary Sources
• Secondary Sources
• Tiertiary Sources
• What Is Scholarly vs. Popular?
• Qualitative Methods
• Quantitative Methods
• Using Non-Textual Elements
• Limitations of the Study
• Common Grammar Mistakes
• Writing Concisely
• Avoiding Plagiarism
• Footnotes or Endnotes?
• Further Readings
• Annotated Bibliography
• Dealing with Nervousness
• Using Visual Aids
• Grading Someone Else's Paper
• Types of Structured Group Activities
• Group Project Survival Skills
• Multiple Book Review Essay
• Reviewing Collected Essays
• Writing a Case Study
• About Informed Consent
• Writing Field Notes
• Writing a Policy Memo
• Writing a Research Proposal
• Bibliography

The term case study refers to both a method of analysis and a specific research design for examining a problem, both of which are used in most circumstances to generalize across populations. This tab focuses on the latter--how to design and organize a research paper in the social sciences that analyzes a specific case.

A case study research paper examines a person, place, event, phenomenon, or other type of subject of analysis in order to extrapolate  key themes and results that help predict future trends, illuminate previously hidden issues that can be applied to practice, and/or provide a means for understanding an important research problem with greater clarity. A case study paper usually examines a single subject of analysis, but case study papers can also be designed as a comparative investigation that shows relationships between two or among more than two subjects. The methods used to study a case can rest within a quantitative, qualitative, or mixed-method investigative paradigm.

Case Studies . Writing@CSU. Colorado State University; Mills, Albert J. , Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010 ; “What is a Case Study?” In Swanborn, Peter G. Case Study Research: What, Why and How? London: SAGE, 2010.

How to Approach Writing a Case Study Research Paper

General information about how to choose a topic to investigate can be found under the " Choosing a Research Problem " tab in this writing guide. Review this page because it may help you identify a subject of analysis that can be investigated using a single case study design.

However, identifying a case to investigate involves more than choosing the research problem . A case study encompasses a problem contextualized around the application of in-depth analysis, interpretation, and discussion, often resulting in specific recommendations for action or for improving existing conditions. As Seawright and Gerring note, practical considerations such as time and access to information can influence case selection, but these issues should not be the sole factors used in describing the methodological justification for identifying a particular case to study. Given this, selecting a case includes considering the following:

• Does the case represent an unusual or atypical example of a research problem that requires more in-depth analysis? Cases often represent a topic that rests on the fringes of prior investigations because the case may provide new ways of understanding the research problem. For example, if the research problem is to identify strategies to improve policies that support girl's access to secondary education in predominantly Muslim nations, you could consider using Azerbaijan as a case study rather than selecting a more obvious nation in the Middle East. Doing so may reveal important new insights into recommending how governments in other predominantly Muslim nations can formulate policies that support improved access to education for girls.
• Does the case provide important insight or illuminate a previously hidden problem? In-depth analysis of a case can be based on the hypothesis that the case study will reveal trends or issues that have not been exposed in prior research or will reveal new and important implications for practice. For example, anecdotal evidence may suggest drug use among homeless veterans is related to their patterns of travel throughout the day. Assuming prior studies have not looked at individual travel choices as a way to study access to illicit drug use, a case study that observes a homeless veteran could reveal how issues of personal mobility choices facilitate regular access to illicit drugs. Note that it is important to conduct a thorough literature review to ensure that your assumption about the need to reveal new insights or previously hidden problems is valid and evidence-based.
• Does the case challenge and offer a counter-point to prevailing assumptions? Over time, research on any given topic can fall into a trap of developing assumptions based on outdated studies that are still applied to new or changing conditions or the idea that something should simply be accepted as "common sense," even though the issue has not been thoroughly tested in practice. A case may offer you an opportunity to gather evidence that challenges prevailing assumptions about a research problem and provide a new set of recommendations applied to practice that have not been tested previously. For example, perhaps there has been a long practice among scholars to apply a particular theory in explaining the relationship between two subjects of analysis. Your case could challenge this assumption by applying an innovative theoretical framework [perhaps borrowed from another discipline] to the study a case in order to explore whether this approach offers new ways of understanding the research problem. Taking a contrarian stance is one of the most important ways that new knowledge and understanding develops from existing literature.
• Does the case provide an opportunity to pursue action leading to the resolution of a problem? Another way to think about choosing a case to study is to consider how the results from investigating a particular case may result in findings that reveal ways in which to resolve an existing or emerging problem. For example, studying the case of an unforeseen incident, such as a fatal accident at a railroad crossing, can reveal hidden issues that could be applied to preventative measures that contribute to reducing the chance of accidents in the future. In this example, a case study investigating the accident could lead to a better understanding of where to strategically locate additional signals at other railroad crossings in order to better warn drivers of an approaching train, particularly when visibility is hindered by heavy rain, fog, or at night.
• Does the case offer a new direction in future research? A case study can be used as a tool for exploratory research that points to a need for further examination of the research problem. A case can be used when there are few studies that help predict an outcome or that establish a clear understanding about how best to proceed in addressing a problem. For example, after conducting a thorough literature review [very important!], you discover that little research exists showing the ways in which women contribute to promoting water conservation in rural communities of Uganda. A case study of how women contribute to saving water in a particular village can lay the foundation for understanding the need for more thorough research that documents how women in their roles as cooks and family caregivers think about water as a valuable resource within their community throughout rural regions of east Africa. The case could also point to the need for scholars to apply feminist theories of work and family to the issue of water conservation.

Eisenhardt, Kathleen M. “Building Theories from Case Study Research.” Academy of Management Review 14 (October 1989): 532-550; Emmel, Nick. Sampling and Choosing Cases in Qualitative Research: A Realist Approach . Thousand Oaks, CA: SAGE Publications, 2013; Gerring, John. “What Is a Case Study and What Is It Good for?” American Political Science Review 98 (May 2004): 341-354; Mills, Albert J. , Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010; Seawright, Jason and John Gerring. "Case Selection Techniques in Case Study Research." Political Research Quarterly 61 (June 2008): 294-308.

Structure and Writing Style

The purpose of a paper in the social sciences designed around a case study is to thoroughly investigate a subject of analysis in order to reveal a new understanding about the research problem and, in so doing, contributing new knowledge to what is already known from previous studies. In applied social sciences disciplines [e.g., education, social work, public administration, etc.], case studies may also be used to reveal best practices, highlight key programs, or investigate interesting aspects of professional work. In general, the structure of a case study research paper is not all that different from a standard college-level research paper. However, there are subtle differences you should be aware of. Here are the key elements to organizing and writing a case study research paper.

I.  Introduction

As with any research paper, your introduction should serve as a roadmap for your readers to ascertain the scope and purpose of your study . The introduction to a case study research paper, however, should not only describe the research problem and its significance, but you should also succinctly describe why the case is being used and how it relates to addressing the problem. The two elements should be linked. With this in mind, a good introduction answers these four questions:

• What was I studying? Describe the research problem and describe the subject of analysis you have chosen to address the problem. Explain how they are linked and what elements of the case will help to expand knowledge and understanding about the problem.
• Why was this topic important to investigate? Describe the significance of the research problem and state why a case study design and the subject of analysis that the paper is designed around is appropriate in addressing the problem.
• What did we know about this topic before I did this study? Provide background that helps lead the reader into the more in-depth literature review to follow. If applicable, summarize prior case study research applied to the research problem and why it fails to adequately address the research problem. Describe why your case will be useful. If no prior case studies have been used to address the research problem, explain why you have selected this subject of analysis.
• How will this study advance new knowledge or new ways of understanding? Explain why your case study will be suitable in helping to expand knowledge and understanding about the research problem.

Each of these questions should be addressed in no more than a few paragraphs. Exceptions to this can be when you are addressing a complex research problem or subject of analysis that requires more in-depth background information.

II.  Literature Review

The literature review for a case study research paper is generally structured the same as it is for any college-level research paper. The difference, however, is that the literature review is focused on providing background information and  enabling historical interpretation of the subject of analysis in relation to the research problem the case is intended to address . This includes synthesizing studies that help to:

• Place relevant works in the context of their contribution to understanding the case study being investigated . This would include summarizing studies that have used a similar subject of analysis to investigate the research problem. If there is literature using the same or a very similar case to study, you need to explain why duplicating past research is important [e.g., conditions have changed; prior studies were conducted long ago, etc.].
• Describe the relationship each work has to the others under consideration that informs the reader why this case is applicable . Your literature review should include a description of any works that support using the case to study the research problem and the underlying research questions.
• Identify new ways to interpret prior research using the case study . If applicable, review any research that has examined the research problem using a different research design. Explain how your case study design may reveal new knowledge or a new perspective or that can redirect research in an important new direction.
• Resolve conflicts amongst seemingly contradictory previous studies . This refers to synthesizing any literature that points to unresolved issues of concern about the research problem and describing how the subject of analysis that forms the case study can help resolve these existing contradictions.
• Point the way in fulfilling a need for additional research . Your review should examine any literature that lays a foundation for understanding why your case study design and the subject of analysis around which you have designed your study may reveal a new way of approaching the research problem or offer a perspective that points to the need for additional research.
• Expose any gaps that exist in the literature that the case study could help to fill . Summarize any literature that not only shows how your subject of analysis contributes to understanding the research problem, but how your case contributes to a new way of understanding the problem that prior research has failed to do.
• Locate your own research within the context of existing literature [very important!] . Collectively, your literature review should always place your case study within the larger domain of prior research about the problem. The overarching purpose of reviewing pertinent literature in a case study paper is to demonstrate that you have thoroughly identified and synthesized prior studies in the context of explaining the relevance of the case in addressing the research problem.

III.  Method

In this section, you explain why you selected a particular subject of analysis to study and the strategy you used to identify and ultimately decide that your case was appropriate in addressing the research problem. The way you describe the methods used varies depending on the type of subject of analysis that frames your case study.

If your subject of analysis is an incident or event . In the social and behavioral sciences, the event or incident that represents the case to be studied is usually bounded by time and place, with a clear beginning and end and with an identifiable location or position relative to its surroundings. The subject of analysis can be a rare or critical event or it can focus on a typical or regular event. The purpose of studying a rare event is to illuminate new ways of thinking about the broader research problem or to test a hypothesis. Critical incident case studies must describe the method by which you identified the event and explain the process by which you determined the validity of this case to inform broader perspectives about the research problem or to reveal new findings. However, the event does not have to be a rare or uniquely significant to support new thinking about the research problem or to challenge an existing hypothesis. For example, Walo, Bull, and Breen conducted a case study to identify and evaluate the direct and indirect economic benefits and costs of a local sports event in the City of Lismore, New South Wales, Australia. The purpose of their study was to provide new insights from measuring the impact of a typical local sports event that prior studies could not measure well because they focused on large "mega-events." Whether the event is rare or not, the methods section should include an explanation of the following characteristics of the event: a) when did it take place; b) what were the underlying circumstances leading to the event; c) what were the consequences of the event.

If your subject of analysis is a person. Explain why you selected this particular individual to be studied and describe what experience he or she has had that provides an opportunity to advance new understandings about the research problem. Mention any background about this person which might help the reader understand the significance of his/her experiences that make them worthy of study. This includes describing the relationships this person has had with other people, institutions, and/or events that support using him or her as the subject for a case study research paper. It is particularly important to differentiate the person as the subject of analysis from others and to succinctly explain how the person relates to examining the research problem.

If your subject of analysis is a place. In general, a case study that investigates a place suggests a subject of analysis that is unique or special in some way and that this uniqueness can be used to build new understanding or knowledge about the research problem. A case study of a place must not only describe its various attributes relevant to the research problem [e.g., physical, social, cultural, economic, political, etc.], but you must state the method by which you determined that this place will illuminate new understandings about the research problem. It is also important to articulate why a particular place as the case for study is being used if similar places also exist [i.e., if you are studying patterns of homeless encampments of veterans in open spaces, why study Echo Park in Los Angeles rather than Griffith Park?]. If applicable, describe what type of human activity involving this place makes it a good choice to study [e.g., prior research reveals Echo Park has more homeless veterans].

If your subject of analysis is a phenomenon. A phenomenon refers to a fact, occurrence, or circumstance that can be studied or observed but with the cause or explanation to be in question. In this sense, a phenomenon that forms your subject of analysis can encompass anything that can be observed or presumed to exist but is not fully understood. In the social and behavioral sciences, the case usually focuses on human interaction within a complex physical, social, economic, cultural, or political system. For example, the phenomenon could be the observation that many vehicles used by ISIS fighters are small trucks with English language advertisements on them. The research problem could be that ISIS fighters are difficult to combat because they are highly mobile. The research questions could be how and by what means are these vehicles used by ISIS being supplied to the militants and how might supply lines to these vehicles be cut? How might knowing the suppliers of these trucks from overseas reveal larger networks of collaborators and financial support? A case study of a phenomenon most often encompasses an in-depth analysis of a cause and effect that is grounded in an interactive relationship between people and their environment in some way.

NOTE:   The choice of the case or set of cases to study cannot appear random. Evidence that supports the method by which you identified and chose your subject of analysis should be linked to the findings from the literature review. Be sure to cite any prior studies that helped you determine that the case you chose was appropriate for investigating the research problem.

IV.  Discussion

The main elements of your discussion section are generally the same as any research paper, but centered around interpreting and drawing conclusions about the key findings from your case study. Note that a general social sciences research paper may contain a separate section to report findings. However, in a paper designed around a case study, it is more common to combine a description of the findings with the discussion about their implications. The objectives of your discussion section should include the following:

Reiterate the Research Problem/State the Major Findings Briefly reiterate the research problem you are investigating and explain why the subject of analysis around which you designed the case study were used. You should then describe the findings revealed from your study of the case using direct, declarative, and succinct proclamation of the study results. Highlight any findings that were unexpected or especially profound.

Explain the Meaning of the Findings and Why They are Important Systematically explain the meaning of your case study findings and why you believe they are important. Begin this part of the section by repeating what you consider to be your most important or surprising finding first, then systematically review each finding. Be sure to thoroughly extrapolate what your analysis of the case can tell the reader about situations or conditions beyond the actual case that was studied while, at the same time, being careful not to misconstrue or conflate a finding that undermines the external validity of your conclusions.

Relate the Findings to Similar Studies No study in the social sciences is so novel or possesses such a restricted focus that it has absolutely no relation to previously published research. The discussion section should relate your case study results to those found in other studies, particularly if questions raised from prior studies served as the motivation for choosing your subject of analysis. This is important because comparing and contrasting the findings of other studies helps to support the overall importance of your results and it highlights how and in what ways your case study design and the subject of analysis differs from prior research about the topic.

Consider Alternative Explanations of the Findings It is important to remember that the purpose of social science research is to discover and not to prove. When writing the discussion section, you should carefully consider all possible explanations for the case study results, rather than just those that fit your hypothesis or prior assumptions and biases. Be alert to what the in-depth analysis of the case may reveal about the research problem, including offering a contrarian perspective to what scholars have stated in prior research.

Acknowledge the Study's Limitations You can state the study's limitations in the conclusion section of your paper but describing the limitations of your subject of analysis in the discussion section provides an opportunity to identify the limitations and explain why they are not significant. This part of the discussion section should also note any unanswered questions or issues your case study could not address. More detailed information about how to document any limitations to your research can be found here .

Suggest Areas for Further Research Although your case study may offer important insights about the research problem, there are likely additional questions related to the problem that remain unanswered or findings that unexpectedly revealed themselves as a result of your in-depth analysis of the case. Be sure that the recommendations for further research are linked to the research problem and that you explain why your recommendations are valid in other contexts and based on the original assumptions of your study.

V.  Conclusion

As with any research paper, you should summarize your conclusion in clear, simple language; emphasize how the findings from your case study differs from or supports prior research and why. Do not simply reiterate the discussion section. Provide a synthesis of key findings presented in the paper to show how these converge to address the research problem. If you haven't already done so in the discussion section, be sure to document the limitations of your case study and needs for further research.

The function of your paper's conclusion is to: 1)  restate the main argument supported by the findings from the analysis of your case; 2) clearly state the context, background, and necessity of pursuing the research problem using a case study design in relation to an issue, controversy, or a gap found from reviewing the literature; and, 3) provide a place for you to persuasively and succinctly restate the significance of your research problem, given that the reader has now been presented with in-depth information about the topic.

Consider the following points to help ensure your conclusion is appropriate:

• If the argument or purpose of your paper is complex, you may need to summarize these points for your reader.
• If prior to your conclusion, you have not yet explained the significance of your findings or if you are proceeding inductively, use the conclusion of your paper to describe your main points and explain their significance.
• Move from a detailed to a general level of consideration of the case study's findings that returns the topic to the context provided by the introduction or within a new context that emerges from your case study findings.

Note that, depending on the discipline you are writing in and your professor's preferences, the concluding paragraph may contain your final reflections on the evidence presented applied to practice or on the essay's central research problem. However, the nature of being introspective about the subject of analysis you have investigated will depend on whether you are explicitly asked to express your observations in this way.

Problems to Avoid

Overgeneralization One of the goals of a case study is to lay a foundation for understanding broader trends and issues applied to similar circumstances. However, be careful when drawing conclusions from your case study. They must be evidence-based and grounded in the results of the study; otherwise, it is merely speculation. Looking at a prior example, it would be incorrect to state that a factor in improving girls access to education in Azerbaijan and the policy implications this may have for improving access in other Muslim nations is due to girls access to social media if there is no documentary evidence from your case study to indicate this. There may be anecdotal evidence that retention rates were better for girls who were on social media, but this observation would only point to the need for further research and would not be a definitive finding if this was not a part of your original research agenda.

Failure to Document Limitations No case is going to reveal all that needs to be understood about a research problem. Therefore, just as you have to clearly state the limitations of a general research study , you must describe the specific limitations inherent in the subject of analysis. For example, the case of studying how women conceptualize the need for water conservation in a village in Uganda could have limited application in other cultural contexts or in areas where fresh water from rivers or lakes is plentiful and, therefore, conservation is understood differently than preserving access to a scarce resource.

Failure to Extrapolate All Possible Implications Just as you don't want to over-generalize from your case study findings, you also have to be thorough in the consideration of all possible outcomes or recommendations derived from your findings. If you do not, your reader may question the validity of your analysis, particularly if you failed to document an obvious outcome from your case study research. For example, in the case of studying the accident at the railroad crossing to evaluate where and what types of warning signals should be located, you failed to take into consideration speed limit signage as well as warning signals. When designing your case study, be sure you have thoroughly addressed all aspects of the problem and do not leave gaps in your analysis.

Case Studies . Writing@CSU. Colorado State University; Gerring, John. Case Study Research: Principles and Practices . New York: Cambridge University Press, 2007; Merriam, Sharan B. Qualitative Research and Case Study Applications in Education . Rev. ed. San Francisco, CA: Jossey-Bass, 1998; Miller, Lisa L. “The Use of Case Studies in Law and Social Science Research.” Annual Review of Law and Social Science 14 (2018): TBD; Mills, Albert J., Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010; Putney, LeAnn Grogan. "Case Study." In Encyclopedia of Research Design , Neil J. Salkind, editor. (Thousand Oaks, CA: SAGE Publications, 2010), pp. 116-120; Simons, Helen. Case Study Research in Practice . London: SAGE Publications, 2009;  Kratochwill,  Thomas R. and Joel R. Levin, editors. Single-Case Research Design and Analysis: New Development for Psychology and Education .  Hilldsale, NJ: Lawrence Erlbaum Associates, 1992; Swanborn, Peter G. Case Study Research: What, Why and How? London : SAGE, 2010; Yin, Robert K. Case Study Research: Design and Methods . 6th edition. Los Angeles, CA, SAGE Publications, 2014; Walo, Maree, Adrian Bull, and Helen Breen. “Achieving Economic Benefits at Local Events: A Case Study of a Local Sports Event.” Festival Management and Event Tourism 4 (1996): 95-106.

Writing Tip

At Least Five Misconceptions about Case Study Research

Social science case studies are often perceived as limited in their ability to create new knowledge because they are not randomly selected and findings cannot be generalized to larger populations. Flyvbjerg examines five misunderstandings about case study research and systematically "corrects" each one. To quote, these are:

Misunderstanding 1 :  General, theoretical [context-independent knowledge is more valuable than concrete, practical (context-dependent) knowledge. Misunderstanding 2 :  One cannot generalize on the basis of an individual case; therefore, the case study cannot contribute to scientific development. Misunderstanding 3 :  The case study is most useful for generating hypotheses; that is, in the first stage of a total research process, whereas other methods are more suitable for hypotheses testing and theory building. Misunderstanding 4 :  The case study contains a bias toward verification, that is, a tendency to confirm the researcher’s preconceived notions. Misunderstanding 5 :  It is often difficult to summarize and develop general propositions and theories on the basis of specific case studies [p. 221].

While writing your paper, think introspectively about how you addressed these misconceptions because to do so can help you strengthen the validity and reliability of your research by clarifying issues of case selection, the testing and challenging of existing assumptions, the interpretation of key findings, and the summation of case outcomes. Think of a case study research paper as a complete, in-depth narrative about the specific properties and key characteristics of your subject of analysis applied to the research problem.

Flyvbjerg, Bent. “Five Misunderstandings About Case-Study Research.” Qualitative Inquiry 12 (April 2006): 219-245.

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Methodology

• What Is a Case Study? | Definition, Examples & Methods

What Is a Case Study? | Definition, Examples & Methods

Published on May 8, 2019 by Shona McCombes . Revised on November 20, 2023.

A case study is a detailed study of a specific subject, such as a person, group, place, event, organization, or phenomenon. Case studies are commonly used in social, educational, clinical, and business research.

A case study research design usually involves qualitative methods , but quantitative methods are sometimes also used. Case studies are good for describing , comparing, evaluating and understanding different aspects of a research problem .

Table of contents

When to do a case study, step 1: select a case, step 2: build a theoretical framework, step 3: collect your data, step 4: describe and analyze the case, other interesting articles.

A case study is an appropriate research design when you want to gain concrete, contextual, in-depth knowledge about a specific real-world subject. It allows you to explore the key characteristics, meanings, and implications of the case.

Case studies are often a good choice in a thesis or dissertation . They keep your project focused and manageable when you don’t have the time or resources to do large-scale research.

You might use just one complex case study where you explore a single subject in depth, or conduct multiple case studies to compare and illuminate different aspects of your research problem.

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See an example

Once you have developed your problem statement and research questions , you should be ready to choose the specific case that you want to focus on. A good case study should have the potential to:

• Provide new or unexpected insights into the subject
• Challenge or complicate existing assumptions and theories
• Propose practical courses of action to resolve a problem
• Open up new directions for future research

TipIf your research is more practical in nature and aims to simultaneously investigate an issue as you solve it, consider conducting action research instead.

Unlike quantitative or experimental research , a strong case study does not require a random or representative sample. In fact, case studies often deliberately focus on unusual, neglected, or outlying cases which may shed new light on the research problem.

Example of an outlying case studyIn the 1960s the town of Roseto, Pennsylvania was discovered to have extremely low rates of heart disease compared to the US average. It became an important case study for understanding previously neglected causes of heart disease.

However, you can also choose a more common or representative case to exemplify a particular category, experience or phenomenon.

Example of a representative case studyIn the 1920s, two sociologists used Muncie, Indiana as a case study of a typical American city that supposedly exemplified the changing culture of the US at the time.

While case studies focus more on concrete details than general theories, they should usually have some connection with theory in the field. This way the case study is not just an isolated description, but is integrated into existing knowledge about the topic. It might aim to:

• Exemplify a theory by showing how it explains the case under investigation
• Expand on a theory by uncovering new concepts and ideas that need to be incorporated
• Challenge a theory by exploring an outlier case that doesn’t fit with established assumptions

To ensure that your analysis of the case has a solid academic grounding, you should conduct a literature review of sources related to the topic and develop a theoretical framework . This means identifying key concepts and theories to guide your analysis and interpretation.

There are many different research methods you can use to collect data on your subject. Case studies tend to focus on qualitative data using methods such as interviews , observations , and analysis of primary and secondary sources (e.g., newspaper articles, photographs, official records). Sometimes a case study will also collect quantitative data.

Example of a mixed methods case studyFor a case study of a wind farm development in a rural area, you could collect quantitative data on employment rates and business revenue, collect qualitative data on local people’s perceptions and experiences, and analyze local and national media coverage of the development.

The aim is to gain as thorough an understanding as possible of the case and its context.

In writing up the case study, you need to bring together all the relevant aspects to give as complete a picture as possible of the subject.

How you report your findings depends on the type of research you are doing. Some case studies are structured like a standard scientific paper or thesis , with separate sections or chapters for the methods , results and discussion .

Others are written in a more narrative style, aiming to explore the case from various angles and analyze its meanings and implications (for example, by using textual analysis or discourse analysis ).

In all cases, though, make sure to give contextual details about the case, connect it back to the literature and theory, and discuss how it fits into wider patterns or debates.

If you want to know more about statistics , methodology , or research bias , make sure to check out some of our other articles with explanations and examples.

• Normal distribution
• Degrees of freedom
• Null hypothesis
• Discourse analysis
• Control groups
• Mixed methods research
• Non-probability sampling
• Quantitative research
• Ecological validity

Research bias

• Rosenthal effect
• Implicit bias
• Cognitive bias
• Selection bias
• Negativity bias
• Status quo bias

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CC0006 Basics of Report Writing

Structure of a report (case study, literature review or survey).

• Structure of report (Site visit)
• Citing Sources
• Tips and Resources

The information in the report has to be organised in the best possible way for the reader to understand the issue being investigated, analysis of the findings and recommendations or implications that relate directly to the findings. Given below are the main sections of a standard report. Click on each section heading to learn more about it.

• Tells the reader what the report is about
• Informative, short, catchy

Example - Sea level rise in Singapore : Causes, Impact and Solution

The title page must also include group name, group members and their matriculation numbers.

Content s Page

• Has headings and subheadings that show the reader where the various sections of the report are located
• Written on a separate page
• Includes the page numbers of each section
• Briefly summarises the report, the process of research and final conclusions
• Provides a quick overview of the report and describes the main highlights
• Short, usually not more than 150 words in length
• Mention briefly why you choose this project, what are the implications and what kind of problems it will solve

Usually, the abstract is written last, ie. after writing the other sections and you know the key points to draw out from these sections. Abstracts allow readers who may be interested in the report to decide whether it is relevant to their purposes.

Introduction

• Discusses the background and sets the context
• Introduces the topic, significance of the problem, and the purpose of research
• Gives the scope ie shows what it includes and excludes

In the introduction, write about what motivates your project, what makes it interesting, what questions do you aim to answer by doing your project. The introduction lays the foundation for understanding the research problem and should be written in a way that leads the reader from the general subject area of the topic to the particular topic of research.

Literature Review

• Helps to gain an understanding of the existing research in that topic
• To develop on your own ideas and build your ideas based on the existing knowledge
• Prevents duplication of the research done by others

Search the existing literature for information. Identify the data pertinent to your topic. Review, extract the relevant information for eg how the study was conducted and the findings. Summarise the information. Write what is already known about the topic and what do the sources that you have reviewed say. Identify conflicts in previous studies, open questions, or gaps that may exist. If you are doing

• Case study - look for background information and if any similar case studies have been done before.
• Literature review - find out from literature, what is the background to the questions that you are looking into
• Site visit - use the literature review to read up and prepare good questions before hand.
• Survey - find out if similar surveys have been done before and what did they find?

Keep a record of the source details of any information you want to use in your report so that you can reference them accurately.

Methodology

Methodology is the approach that you take to gather data and arrive at the recommendation(s). Choose a method that is appropriate for the research topic and explain it in detail.

In this section, address the following: a) How the data was collected b) How it was analysed and c) Explain or justify why a particular method was chosen.

Usually, the methodology is written in the past tense and can be in the passive voice. Some examples of the different methods that you can use to gather data are given below. The data collected provides evidence to build your arguments. Collect data, integrate the findings and perspectives from different studies and add your own analysis of its feasibility.

• Explore the literature/news/internet sources to know the topic in depth
• Give a description of how you selected the literature for your project
• Compare the studies, and highlight the findings, gaps or limitations.
• An in-depth, detailed examination of specific cases within a real-world context.
• Enables you to examine the data within a specific context.
• Examine a well defined case to identify the essential factors, process and relationship.
• Write the case description, the context and the process involved.
• Make sense of the evidence in the case(s) to answer the research question
• Gather data from a predefined group of respondents by asking relevant questions
• Can be conducted in person or online
• Why you chose this method (questionnaires, focus group, experimental procedure, etc)
• How you carried out the survey. Include techniques and any equipment you used
• If there were participants in your research, who were they? How did you select them and how may were there?
• How the survey questions address the different aspects of the research question
• Analyse the technology / policy approaches by visiting the required sites
• Make a detailed report on its features and your understanding of it

Results and Analysis

• Present the results of the study. You may consider visualising the results in tables and graphs, graphics etc.
• Analyse the results to obtain answer to the research question.
• Provide an analysis of the technical and financial feasibility, social acceptability etc

Discussion, Limitation(s) and Implication(s)

• Discuss your interpretations of the analysis and the significance of your findings
• Explain any new understanding or insights that emerged as a result of your research
• Consider the different perspectives (social, economic and environmental)in the discussion
• Explain the limitation(s)
• Explain how could what you found be used to make a difference for sustainability

Conclusion and Recommendations

• Summarise the significance and outcome of the study highlighting the key points.
• Come up with alternatives and propose specific actions based on the alternatives
• Describe the result or improvement it would achieve
• Explain how it will be implemented

Recommendations should have an innovative approach and should be feasible. It should make a significant difference in solving the issue under discussion.

• List the sources you have referred to in your writing
• Use the recommended citation style consistently in your report

Appendix (if necessary/any)

Include any material relating to the report and research that does not fit in the body of the report, in the appendix. For example, you may include survey questionnaire and results in the appendix.

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• Case Study | Definition, Examples & Methods

Case Study | Definition, Examples & Methods

Published on 5 May 2022 by Shona McCombes . Revised on 30 January 2023.

A case study is a detailed study of a specific subject, such as a person, group, place, event, organisation, or phenomenon. Case studies are commonly used in social, educational, clinical, and business research.

A case study research design usually involves qualitative methods , but quantitative methods are sometimes also used. Case studies are good for describing , comparing, evaluating, and understanding different aspects of a research problem .

Table of contents

When to do a case study, step 1: select a case, step 2: build a theoretical framework, step 3: collect your data, step 4: describe and analyse the case.

A case study is an appropriate research design when you want to gain concrete, contextual, in-depth knowledge about a specific real-world subject. It allows you to explore the key characteristics, meanings, and implications of the case.

Case studies are often a good choice in a thesis or dissertation . They keep your project focused and manageable when you don’t have the time or resources to do large-scale research.

You might use just one complex case study where you explore a single subject in depth, or conduct multiple case studies to compare and illuminate different aspects of your research problem.

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Once you have developed your problem statement and research questions , you should be ready to choose the specific case that you want to focus on. A good case study should have the potential to:

• Provide new or unexpected insights into the subject
• Challenge or complicate existing assumptions and theories
• Propose practical courses of action to resolve a problem
• Open up new directions for future research

Unlike quantitative or experimental research, a strong case study does not require a random or representative sample. In fact, case studies often deliberately focus on unusual, neglected, or outlying cases which may shed new light on the research problem.

If you find yourself aiming to simultaneously investigate and solve an issue, consider conducting action research . As its name suggests, action research conducts research and takes action at the same time, and is highly iterative and flexible. 

However, you can also choose a more common or representative case to exemplify a particular category, experience, or phenomenon.

While case studies focus more on concrete details than general theories, they should usually have some connection with theory in the field. This way the case study is not just an isolated description, but is integrated into existing knowledge about the topic. It might aim to:

• Exemplify a theory by showing how it explains the case under investigation
• Expand on a theory by uncovering new concepts and ideas that need to be incorporated
• Challenge a theory by exploring an outlier case that doesn’t fit with established assumptions

To ensure that your analysis of the case has a solid academic grounding, you should conduct a literature review of sources related to the topic and develop a theoretical framework . This means identifying key concepts and theories to guide your analysis and interpretation.

There are many different research methods you can use to collect data on your subject. Case studies tend to focus on qualitative data using methods such as interviews, observations, and analysis of primary and secondary sources (e.g., newspaper articles, photographs, official records). Sometimes a case study will also collect quantitative data .

The aim is to gain as thorough an understanding as possible of the case and its context.

In writing up the case study, you need to bring together all the relevant aspects to give as complete a picture as possible of the subject.

How you report your findings depends on the type of research you are doing. Some case studies are structured like a standard scientific paper or thesis, with separate sections or chapters for the methods , results , and discussion .

Others are written in a more narrative style, aiming to explore the case from various angles and analyse its meanings and implications (for example, by using textual analysis or discourse analysis ).

In all cases, though, make sure to give contextual details about the case, connect it back to the literature and theory, and discuss how it fits into wider patterns or debates.

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• Five tips for developing useful literature summary tables for writing review articles
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• http://orcid.org/0000-0003-0157-5319 Ahtisham Younas 1 , 2 ,
• http://orcid.org/0000-0002-7839-8130 Parveen Ali 3 , 4
• 1 Memorial University of Newfoundland , St John's , Newfoundland , Canada
• 2 Swat College of Nursing , Pakistan
• 3 School of Nursing and Midwifery , University of Sheffield , Sheffield , South Yorkshire , UK
• 4 Sheffield University Interpersonal Violence Research Group , Sheffield University , Sheffield , UK
• Correspondence to Ahtisham Younas, Memorial University of Newfoundland, St John's, NL A1C 5C4, Canada; ay6133{at}mun.ca

https://doi.org/10.1136/ebnurs-2021-103417

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Introduction

Literature reviews offer a critical synthesis of empirical and theoretical literature to assess the strength of evidence, develop guidelines for practice and policymaking, and identify areas for future research. 1 It is often essential and usually the first task in any research endeavour, particularly in masters or doctoral level education. For effective data extraction and rigorous synthesis in reviews, the use of literature summary tables is of utmost importance. A literature summary table provides a synopsis of an included article. It succinctly presents its purpose, methods, findings and other relevant information pertinent to the review. The aim of developing these literature summary tables is to provide the reader with the information at one glance. Since there are multiple types of reviews (eg, systematic, integrative, scoping, critical and mixed methods) with distinct purposes and techniques, 2 there could be various approaches for developing literature summary tables making it a complex task specialty for the novice researchers or reviewers. Here, we offer five tips for authors of the review articles, relevant to all types of reviews, for creating useful and relevant literature summary tables. We also provide examples from our published reviews to illustrate how useful literature summary tables can be developed and what sort of information should be provided.

Tip 1: provide detailed information about frameworks and methods

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Tabular literature summaries from a scoping review. Source: Rasheed et al . 3

The provision of information about conceptual and theoretical frameworks and methods is useful for several reasons. First, in quantitative (reviews synthesising the results of quantitative studies) and mixed reviews (reviews synthesising the results of both qualitative and quantitative studies to address a mixed review question), it allows the readers to assess the congruence of the core findings and methods with the adapted framework and tested assumptions. In qualitative reviews (reviews synthesising results of qualitative studies), this information is beneficial for readers to recognise the underlying philosophical and paradigmatic stance of the authors of the included articles. For example, imagine the authors of an article, included in a review, used phenomenological inquiry for their research. In that case, the review authors and the readers of the review need to know what kind of (transcendental or hermeneutic) philosophical stance guided the inquiry. Review authors should, therefore, include the philosophical stance in their literature summary for the particular article. Second, information about frameworks and methods enables review authors and readers to judge the quality of the research, which allows for discerning the strengths and limitations of the article. For example, if authors of an included article intended to develop a new scale and test its psychometric properties. To achieve this aim, they used a convenience sample of 150 participants and performed exploratory (EFA) and confirmatory factor analysis (CFA) on the same sample. Such an approach would indicate a flawed methodology because EFA and CFA should not be conducted on the same sample. The review authors must include this information in their summary table. Omitting this information from a summary could lead to the inclusion of a flawed article in the review, thereby jeopardising the review’s rigour.

Tip 2: include strengths and limitations for each article

Critical appraisal of individual articles included in a review is crucial for increasing the rigour of the review. Despite using various templates for critical appraisal, authors often do not provide detailed information about each reviewed article’s strengths and limitations. Merely noting the quality score based on standardised critical appraisal templates is not adequate because the readers should be able to identify the reasons for assigning a weak or moderate rating. Many recent critical appraisal checklists (eg, Mixed Methods Appraisal Tool) discourage review authors from assigning a quality score and recommend noting the main strengths and limitations of included studies. It is also vital that methodological and conceptual limitations and strengths of the articles included in the review are provided because not all review articles include empirical research papers. Rather some review synthesises the theoretical aspects of articles. Providing information about conceptual limitations is also important for readers to judge the quality of foundations of the research. For example, if you included a mixed-methods study in the review, reporting the methodological and conceptual limitations about ‘integration’ is critical for evaluating the study’s strength. Suppose the authors only collected qualitative and quantitative data and did not state the intent and timing of integration. In that case, the strength of the study is weak. Integration only occurred at the levels of data collection. However, integration may not have occurred at the analysis, interpretation and reporting levels.

Tip 3: write conceptual contribution of each reviewed article

While reading and evaluating review papers, we have observed that many review authors only provide core results of the article included in a review and do not explain the conceptual contribution offered by the included article. We refer to conceptual contribution as a description of how the article’s key results contribute towards the development of potential codes, themes or subthemes, or emerging patterns that are reported as the review findings. For example, the authors of a review article noted that one of the research articles included in their review demonstrated the usefulness of case studies and reflective logs as strategies for fostering compassion in nursing students. The conceptual contribution of this research article could be that experiential learning is one way to teach compassion to nursing students, as supported by case studies and reflective logs. This conceptual contribution of the article should be mentioned in the literature summary table. Delineating each reviewed article’s conceptual contribution is particularly beneficial in qualitative reviews, mixed-methods reviews, and critical reviews that often focus on developing models and describing or explaining various phenomena. Figure 2 offers an example of a literature summary table. 4

Tabular literature summaries from a critical review. Source: Younas and Maddigan. 4

Tip 4: compose potential themes from each article during summary writing

While developing literature summary tables, many authors use themes or subthemes reported in the given articles as the key results of their own review. Such an approach prevents the review authors from understanding the article’s conceptual contribution, developing rigorous synthesis and drawing reasonable interpretations of results from an individual article. Ultimately, it affects the generation of novel review findings. For example, one of the articles about women’s healthcare-seeking behaviours in developing countries reported a theme ‘social-cultural determinants of health as precursors of delays’. Instead of using this theme as one of the review findings, the reviewers should read and interpret beyond the given description in an article, compare and contrast themes, findings from one article with findings and themes from another article to find similarities and differences and to understand and explain bigger picture for their readers. Therefore, while developing literature summary tables, think twice before using the predeveloped themes. Including your themes in the summary tables (see figure 1 ) demonstrates to the readers that a robust method of data extraction and synthesis has been followed.

Tip 5: create your personalised template for literature summaries

Often templates are available for data extraction and development of literature summary tables. The available templates may be in the form of a table, chart or a structured framework that extracts some essential information about every article. The commonly used information may include authors, purpose, methods, key results and quality scores. While extracting all relevant information is important, such templates should be tailored to meet the needs of the individuals’ review. For example, for a review about the effectiveness of healthcare interventions, a literature summary table must include information about the intervention, its type, content timing, duration, setting, effectiveness, negative consequences, and receivers and implementers’ experiences of its usage. Similarly, literature summary tables for articles included in a meta-synthesis must include information about the participants’ characteristics, research context and conceptual contribution of each reviewed article so as to help the reader make an informed decision about the usefulness or lack of usefulness of the individual article in the review and the whole review.

In conclusion, narrative or systematic reviews are almost always conducted as a part of any educational project (thesis or dissertation) or academic or clinical research. Literature reviews are the foundation of research on a given topic. Robust and high-quality reviews play an instrumental role in guiding research, practice and policymaking. However, the quality of reviews is also contingent on rigorous data extraction and synthesis, which require developing literature summaries. We have outlined five tips that could enhance the quality of the data extraction and synthesis process by developing useful literature summaries.

• Aromataris E ,
• Rasheed SP ,

Twitter @Ahtisham04, @parveenazamali

Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

Competing interests None declared.

Patient consent for publication Not required.

Provenance and peer review Not commissioned; externally peer reviewed.

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What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

• What is the purpose of literature review? 
• a. Habitat Loss and Species Extinction: 
• b. Range Shifts and Phenological Changes: 
• c. Ocean Acidification and Coral Reefs: 
• d. Adaptive Strategies and Conservation Efforts: 
• How to write a good literature review 
• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• Frequently asked questions 

What is a literature review?

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

What is the purpose of literature review?

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

• Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 
• Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field. 
• Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 
• Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 
• Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 
• Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

a. Habitat Loss and Species Extinction:

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

b. Range Shifts and Phenological Changes:

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

c. Ocean Acidification and Coral Reefs:

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

d. Adaptive Strategies and Conservation Efforts:

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

How to write a good literature review

Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. 

Frequently asked questions

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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A Review of the Literature on Case Study Research

This paper presents a review of the literature on case study research and comments on the ongoing debate of the value of case study. A research paradigm and its theoretical framework is described. This review focuses extensively on the positions of

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Literature review as a key step in research processes: case study of MA dissertations written on EFL of Saudi context

Saudi Journal of Language Studies

ISSN : 2634-243X

Article publication date: 1 June 2022

Issue publication date: 4 August 2022

The aim of this study is to find out the most common types of literature review and the accuracy of citing information related to topic in question among Saudi English as a Foreign Language (EFL) postgraduate students at Al-Baha University. This study also aims at revealing the quality of the literature review written by researchers.

Design/methodology/approach

This qualitative study used content analysis to investigate 15 unpublished Master of Arts (MA) dissertations written on EFL of Saudi context. They were analyzed qualitatively using criteria modified from Snyder's (2019) model which is considered a potential method for making theoretical and practical contributions of literature review.

The findings of the study showed that students favored the systematic review over the integrative. Additionally, data showed that students were lacking in paraphrasing and organizing cited information coherently and appropriately. Moreover, students' performance was better in design, conduct, and data abstraction and analysis criterion, whereas they seemed rather weak in structuring and writing the review criteria.

Originality/value

The significance of the study is to provide researchers with methodological guidance and reference to write a comprehensive and appropriate literature review. Based on the findings, this study concluded with some implications that aim to assist researchers in carrying out their studies professionally. Furthermore, the findings provide decision-makers in higher education institutions with important practical implications. In light of the study's findings, it is suggested to carry out further research investigating postgraduate students to find out their perceptions and attitudes regarding the quality standards of scientific research writing and the paraphrasing strategies.

• MA students
• Literature review

Integrative review

Semi-systematic review.

• Systematic review
• Literature review quality
• Paraphrasing

Alsalami, A.I. (2022), "Literature review as a key step in research processes: case study of MA dissertations written on EFL of Saudi context", Saudi Journal of Language Studies , Vol. 2 No. 3, pp. 153-169. https://doi.org/10.1108/SJLS-04-2022-0044

Emerald Publishing Limited

Copyright © 2022, Ahmed Ibrahim Alsalami

Published in Saudi Journal of Language Studies . Published by Emerald Publishing Limited. This article is published under the Creative Commons Attribution (CC BY 4.0) licence. Anyone may reproduce, distribute, translate and create derivative works of this article (for both commercial and non-commercial purposes), subject to full attribution to the original publication and authors. The full terms of this licence may be seen at http://creativecommons.org/licences/by/4.0/legalcode

Introduction

The way a researcher is building his/her research and linking it to current knowledge is like building a block of academic research activity, no matter which discipline it relates to, thus it is a priority step ( Snyder, 2019 ). In a definition by Liberati et al. (2009) cited in Snyder (2019) “ A systematic review can be explained as a research method and process for identifying and critically appraising relevant research, as well as for collecting and analyzing data from said research .” (p. 334). A literature review is an important part of any research as it is considered a foundation of the type of research.

As in Snyder (2019) , literature review is a written text of a published study that includes current knowledge and up-to-date information about the latest findings of science on a particular topic, including substantial discoveries as well as theoretical and practical contributions from scholarly research groups. A literature review as defined by Hart (1998) (Cronin et al ., 2008 cited in Ramdhani et al ., 2014 ) “ is an objective and thorough summary and critical analysis of the relevant, available research and non-research literature on the topic being studied ” (p. 48). A literature review requires a compound series of abilities to learn topics to explore and acquire and retrieve literature searching skills. Additionally, it requires the ability to develop, analyze and synthesize data to be keen on reporting and writing normally at a limited scale of time. Scholars divided the literature review into two types. The first is “Traditional or Narrative Literature Review”. This type of review criticizes and summarizes the body of the literature to draw conclusions about the topic under consideration. The basic aim of this review is to support a reviewer with a complete review to understand the knowledge and to show the implication of new inquiries. The second one is “Systematic Literature Review” which reviews the literature in a specific subject area to employ a more rigorous and well-defined approach. A systematic literature review is often used to solve a specific medical practice question ( Parahoo, 2006 ; Davis et al ., 2014 ; Almelhes, 2020 ). Some studies regard “meta-analysis” as a type of systematic review, which is primarily a statistical method that entails evaluating the research results among many studies on the very same topic using standardized statistical tests in drawing conclusions and identify patterns and trends between research results ( Polit and Beck, 2006 ; Dundar and Fleeman, 2017 ; Almelhes, 2020 ).

The most common types of literature review among Saudi EFL postgraduate students in Al-Baha University,

The accuracy of citing information related to the topic in question and

The quality of the literature review written by the MA researchers at Al-Baha University.

What are the most common types of literature review among Saudi EFL students at Al-Baha University?

To what extent is the accuracy of citing information related to the topic in question?

To what extent is the quality of the literature review written by the MA researchers at Al-Baha University?

Steps and phases of doing a literature review

Designing the review.

Why should this literature be reviewed? Do we really need literature in this area of our topic? And what literature review would be the great type for contribution? Indeed, these questions would be better borne in the mind of a researcher before starting to review the literature because they determine the likelihood of the review and the impact it might have on the research community ( Antons and Breidbach, 2018 ). As it is a hard work to conduct a literature review, the topic must interest both author and the reader. Hence, first of all, it is better to scan the points to relate to existing knowledge. Moreover, Palmatier et al . (2018) stated that any criterion related to the on-focus topic should be directed by the research questions.

Conducting the review

Conducting a review is required after deciding on the purpose, questions and type of approach that better suits the topic in question. Additionally, it is better to appropriately test the review process and protocol before performing the main review. To ensure the quality and reliability of the search protocol, it is important to use two reviewers to select articles depending on the nature and scope of the review ( Antons and Breidbach, 2018 ; Almelhes, 2020 ).

Analyzing the literature

To conduct appropriate analysis, it is important to consider how the articles will be used. Meanwhile, abstracting information needs to be professionally measured ( Palmatier et al ., 2018 ). They can be put into descriptive information (e.g. authors, year of publication, topic or type of study), or in effects and findings format, conceptualizations or theoretical perspective. Additionally, it is better to avoid any differences in coding and monitoring the data abstraction carefully during the review process in order to ensure quality and reliability. Researchers should ensure that their literature is appropriate to answer the selected research question.

Writing a review

The final review of any article depends on an approach that requires types of different information and different levels of details like standards and guidelines that explicitly address how literature reviews should be reported and structured (see Table 1 , below). Standards and guidelines for systematic narrative reviews ( Wong et al. , 2013 ) or guidelines for integrative reviews ( Torraco, 2005 ) should be considered in the final review too. Moreover, how literature was identified, analyzed, synthesized and reported by a researcher is necessary to describe transparently the process of designing the review literature. Literature reviews can result in a historical analysis of the development within a research field ( Carlborg et al ., 2014 ; Almelhes, 2020 ) or can be any agendas for further research ( McColl-Kennedy et al. , 2017 ), besides, conceptual model or categorization ( Snyder et al. , 2016 ; Witell et al ., 2016 ), or can be evidence of an effect ( Verlegh and Steenkamp, 1999 ).

The process of undertaking a literature review

Regardless of the method used to carry out the literature review, there seems to be a myriad of activities to be carried out and decisions made in order to build an assessment that satisfies the criteria for publication (for specific considerations with regards to each phase, as seen in Table 2 ). There are four phases that demonstrate and discuss the essential decisions and questions associated with conducting a literature review (as in Table 2 below): (1) designing the review, (2) conducting the review, (3) analysis and (4) structuring and writing the review ( Snyder, 2019 ). This procedure arose from real-world and practical experience and is a synthesis of and impact by diverse rules and specifications for literature reviews (e.g. Liberati et al. , 2009 ; Tranfield et al. , 2003 ; Wong et al. , 2013 ).

Types of literature review

Systematic literature review.

As described by Davis et al. , (2014) and later by Dundar and Fleeman (2017) , systematic reviews have first developed within medical sciences to synthesize research findings in a systematic, transparent and reproducible way. It can be a process for identifying and critically appraising relevant research for collecting and analyzing data from previous studies ( Liberati et al. , 2009 ; Almelhes, 2020 ). It aimed at identifying all empirical evidence that fits the pre-specified inclusion criteria to answer a particular research question or hypothesis. Bias can be minimized to provide reliable findings from conclusions and decisions ( Liberati et al. , 2009 ). Often statistical approaches are used to integrate the results of the topics in question. It combines results from different studies to evaluate and compare and identify patterns, disagreements or relationships ( Davis et al. , 2014 ) to assess them. It can be used to determine the continuity of effects across studies and to discover types of future studies that are required to be conducted to demonstrate the effect. Besides, techniques were used to discover which study-level or sample characteristics affect the phenomenon ( Davis et al. , 2014 ). The primary goal of a systematic review is to provide as comprehensive a list as possible of all studies whether published or unpublished, and these studies concerning a specific subject ( Ryan et al ., 2007 ; Dundar and Fleeman, 2017 ).

A systematic review needs to use standards as a roadmap for collecting studies ( Livinski et al ., 2015 ). Systematic review design has covered the following criteria: (1) studies related to students' attitudes; (2) the engagement of the learning process and (3) the outcomes of studies regarding speaking, writing and reading skills ( Antons and Breidbach, 2018 ; Almelhes, 2020 ).

The semi-systematic or narrative review approach hinders a full systematic review process. It is designed for different conceptualized and various studies that were studied by groups of researchers within various disciplines ( Wong et al. , 2013 ; Dundar and Fleeman, 2017 ).

Since it is hard to review every single article relevant to the topic, a different strategy must be developed ( McColl-Kennedy et al. , 2017 ). It aims at overviewing a topic and how research has progressed over time and developed. Generally, it seeks to identify and understand all potentially relevant research traditions and synthesize them by measuring effect size ( Wong et al. , 2013 ) and provides a considerate understanding of complex areas. It is potentially contributed to a useful analysis for detecting themes, and theoretical viewpoints of specific research disciplines as well as to identifying components of a theoretical concept ( Ward et al ., 2009 ). Thus, gain the ability to map a field of research, synthesize the state of knowledge and create an agenda for further research or the ability to provide a historical overview of a specific topic.

An integrative review is closely related to the semi-structured (integrative or critical review) approach. Usually, it has a different purpose from the semi-structured review which aims to assess, critique, and synthesize the literature in a way to develop new theoretical frameworks and perspectives ( Torraco, 2005 ). Generally, integrative literature reviews are intended to address mature or new topics. Additionally, seek to emerge topics to overview the knowledge base, critically review and potentially reconceptualize and expand on the theoretical foundation of the specific topic. It requires a more creative collection of data ( Whittemore and Knafl, 2005 ). A review of good literature does not summarize the sources, but rather analyzes, collects and evaluates them accurately to form a clear and general picture of existing knowledge or science on this topic.

Text borrowing skills

Text borrowing and incorporating other people's written ideas into one's own scholarly work are useful qualities to have in the world of academia, particularly for those pursuing higher education. Text borrowing expertise widely used in academic writing includes direct quoting, paraphrasing and summarizing. When contrasted to paraphrasing, directly quoting from the primary material is far more feasible, easier and less complex. There is really nothing inappropriate with integrating quotations; nevertheless, as Davis and Beaumont (2007) point out, overusing quotations does not really represent highly proficient writing. Rather, academic writing motivates the use of paraphrasing, drawing conclusions or synthesizing skill sets.

Paraphrasing is described as reiterating a statement in such a manner that both sentences are lexically and syntactically distinct whilst also remaining semantically equivalent ( Amoroso, 2007 ; Davis and Beaumont, 2007 ; McCarthy et al ., 2009 ). At least two echoes are implied by this description: reading process skills and writing ability. As a result, according to McCarthy et al . (2009) , paraphrasing is often used to aid comprehension, enhance previous knowledge and assist the development of writing skills.

According to cognitive psychology literature, paraphrasing is mentally demanding. As the content to be paraphrased has become more complicated, students are more likely to use simplified processing, resulting in patchwork written text (Marsh, Landau and Hick in Walker, 2008 ). Walker adds that just imagining about paraphrasing takes a substantial amount of cognitive vitality, and when the physical writing process starts, individuals have restricted opportunity to undertake thoughtful, systematic processing to ascertain if they paraphrased correctly. These complicated characteristics of paraphrasing cause some challenges. In the Japanese context, Iwasaki (1999) discovered four major areas of difficulty: varying behavioral patterns of parts of speech, subject limitation, context-specific paraphrasing and “blank” locating. There seems to be little proof, and data obtained from extensive research dedicated to examining paraphrasing-related concerns in the Indonesian context. Despite an abundance of survey participants, Kusumasondjaja's (2010) survey did not test students' paraphrasing abilities. It appears that paraphrasing is not represented, is described vaguely or is purely regarded as changing the existing source without stating the extent of adjustment.

In the Saudi context, Alaofi (2020) investigated the key problems that Saudi graduate students usually face when summarizing and paraphrasing source texts in EFL. Nine Saudi students attending university degrees in multiple fields were questioned using a qualitative approach. The study's findings revealed that a variety of barriers may exacerbate students' challenges with the skills under examination. These were students' insufficient English proficiency is the first root of complexities in summarizing and paraphrasing original text, followed by issues with students' writing styles and, finally, poor reading comprehension skillsets.

Methodology

As mentioned above, the purpose of this study is to analyze and synthesize findings from the content that is written in the literature review section of 15 unpublished MA studies. These studies were written in the Saudi context and conducted by MA postgraduate students of Al-Baha University. Additionally, to find out the most common types of literature review used by Saudi EFL postgraduate students in Al-Baha University, and to measure the accuracy of citing information related to topics in question, besides finding out the criteria and assess the quality of literature review written by MA researchers, to come out with rich findings that can guide undergraduate students in writing and reviewing knowledge related to their theses and research papers. Additionally, it can help postgraduates and other academic researchers to build a tidy content of literature and coherent procedures for research writing. Thus, this research is done qualitatively using content analysis taking into account the discipline, type of literature review, and contribution to see how successfully these researchers attract readers' attention and satisfy their needs, and in the long run, increase the quality of research and to develop better and more accurate hypotheses and questions.

To measure the research questions, 15 MA dissertations were selected randomly and carefully analyzed accordingly. The analysis of these 15 studies focused mainly on finding out the common types of literature review used by Saudi EFL students in Al-Baha University, and finding the accuracy of citing information, besides assessing the quality of the literature review of the selected MA research. Synder's (2019) model for assessing the quality of literature review is used as a criterion to analyze these MA studies. All are written in the field of English Language Teaching (ELT) settings. Therefore, it will be a potential step in making theoretical and practical contributions to literature review as a method to clarify what a literature review is, how it can be used and what criteria should be used to evaluate its quality. Thus, in this paper, the contribution differentiates between several types of literature review methodologies such as systematic, semi-systematic, and traditional/integrative approaches and how the procedures and the quality were shown (see Appendix ). Besides, presenting real practices that may be met when reviewing literature in EFL research. Additionally, it provides context and guidance to students and academics to use the literature review as a method to synthesize their research in question.

As in Appendix , the criteria used contained four phases: (1) design (includes 6 dimensions); (2) conduct (includes 5 dimensions); (3) data abstraction and analysis (includes 5 dimensions); and (4) structuring and writing the review (includes 5 dimensions). To show that the criterion has been met, the researcher used the symbol (√) as an indication system or vice versa (×) if it was not. The 15 kinds of research were coded using numbers (i.e. each research was given a number from 1 to 15). Then each research was checked according to the dimension of each criterion of each quality. These 15 unpublished MA studies were collected from the College of Arts and Humanities in Al Aqiq main campus, where the postgraduate dissertations were archived, and these studies were conducted during the period from 2013 to 2018. The reason for not selecting newer studies after 2018 is that this paid master's program has been discontinued and has resumed in mid-2021. To ensure the quality of the assessment and the analysis according to Synder's standard, the researcher got help from jury members of three PhD holders (voluntarily) who work in the Department of English at the College of Science and Arts in Qilwah. They had more than ten years of experience in the field of teaching and scientific research. The research took place in a round-held table for a number of meetings and asked them to review and evaluate the MA research according to Synder's criteria. The evaluation continued for three months, and each phase and its dimensions were discussed in separate sessions. The evaluation and discussion took place during the first term of the academic year 2021. Step by step the researcher continuously discussed with the jury members their evaluation (see Appendix ).

The analysis section was divided into two parts. The first part displayed the data gathered to measure the first and the second questions, whereas the second part displayed the third question.

Discovering common types of literature review and evaluating the accuracy of citing information

Part 1 : The main types of literature review (traditional or narrative, systematic, meta-analysis and meta-synthesis) were scrutinized and analyzed in light of their qualities and procedures. In this paper, three types are chosen to be judged accordingly. They are systematic, semi-systematic and traditional/integrative approaches. As mentioned above, the 15 MA projects were handed over to the reviewers (the researcher's colleagues). After long and regular sessions, they concluded their results to the researcher. They revealed that studies 1, 10 and 15 showed a masterpiece reflection of the systematic review approach. In this sense, these studies synthesized and compared evidence between the two studies. Another example is that these studies in the introduction section produced a clear and rationale connection between the topic and literature written in the same field of the study. These studies also showed that the information provided is reliable and based on proven facts. Additionally, the information is verified against other reliable sources. To be more realistic, we must evaluate all sources before deciding whether to incorporate what was found into the literature review ( Synder, 2019 ). Moreover, resources need to be evaluated to make sure that they contain information, which is valuable and pertinent, in this point, this study is consistent with what was found by other researchers ( Liberati et al. , 2009 ; Tranfield et al. , 2003 ; Wong et al. , 2013 ; Synder, 2019 ). These studies presented a rich literature that is displayed in various types of periodicals that include scholarly journals of high impact factors and intensive readability.

Generally, studies (1, 3, 4, 6, 8, 10, 11, 12, 13, 14 and 15) used systematic reviews to answer their highly structured and specific research questions. They undertook a more rigorous approach in reviewing the literature they presented in their research. In contrast, a traditional or narrative literature review usually adopts a critical approach in a way that analyzes and summarizes to address intensive information to shed light on new ideas, bridge gaps or/and cover weaknesses of previous research, studies endeavored a very high and accurate criterion of evaluating literature review Ryan et al. (2007) . On the other hand, studies (2, 5, 7 and 9) used both semi-systematic and integrative/traditional literature reviews. This clearly showed that the research questions were broad. On the other hand, in the introduction section, these studies used a semi-systematic literature review. For accuracy purposes, these studies presented a piece of reliable information. All the information displayed in these studies was error-free. Additionally, it is easy to say that the information shown was based on proven facts and can be verified against other reliable sources. All that cited in these studies in the literature review section was taken from famous and well-known periodicals. They can be completely described as facts shown without any bias. When looking back to what the researchers presented, it is easy to see that information presented was currently published to show the currency matter of the researchers' topics. The coverage of information has met in-depth the information needed to build up a literature review process. Accordingly, the researchers reviewed rich and accurate literature written about the focus topics to rationalize their objectives in conducting their research. All the information shown by researchers was presented without any bias. Thus, each study presented more than four references to show the accurateness of the literature. Additionally, the information presented is highly met and covered the needed information, and provided a basic and in-depth coverage. To meet the aims of systematic review (as in Dundar and Fleeman, 2017 ), to some extent, these studies provided a complete list of all possible published and unpublished studies relating to the researcher's subject matter.

To deal with the accuracy of citing information, in studies (2, 3, 4, 5, 9, 10, 11, 12, 14 and 15) one can find that, from the beginning, in the introduction section, these studies started citing from very recently published researches. Most interestingly, the researchers used the paraphrasing method to cite information related to the researchers' topic. However, they did not paraphrase appropriately. These studies used a paraphrasing method to make the information cited more reliable, error-free, based on proven facts and can be verified against other reliable sources. In this sense, these studies presented information that can be more accurate. But unexpectedly, those who used the paraphrasing method lacked professionality in treating the original text and formulating it using their own words (i.e. there is an apparent weakness in meaning between the original source and the paraphrased text). Again, the studies showed that researchers intended the purpose of the information in a precise way initiating that in the introduction. The studies also presented facts that were proven by famous writers.

Assessing the quality of a literature review

Part 2: As empirical research, literature reviews need assessment and evaluation ( Palmatier et al. , 2018 ). The literature review quality must have both depth and rigor to determine a suitable strategy for choosing topics and apprehending data and insights and to recite previous studies slightly. The quality of the literature review needs to be replicable to make the reader easily replicate the topic and reaches similar findings. Additionally, they must be useful for scholars and practitioners. Normally, the evaluation of different types of literature reviews is considered to be challenging. However, some guidelines could be used as a starting point to help researchers in evaluating literature reviews, to examine and to assess the review criteria for rigor and depth. To assess the literature review quality related to MA studies (the 15 selected samples) in question, Snyder (2019 , p. 338) suggested some guidelines as seen in Appendix .

Therefore, to find out a suitable step-by-step approach that can guide students and academics in undertaking a valid, comprehensive and helpful literature review, appropriate literature reviews have been gathered for this inquiry to investigate the criteria and quality of literature presented by selected MA studies (see Appendix ). Depending on the purpose of the topic, various literature studies may be highly useful to suggest which strategy may suit the analysis and synthesis stages that greatly help in the selection and writing of the literature review on EFL context, mainly Saudi context. Thus, the selected reviews were scrutinized and analyzed considering their qualities and procedures. In this paper, only 15 MA studies were chosen to be measured accordingly.

As in Appendix , the quality of these projects was checked and graded by the reviewers (the researchers' colleagues). Looking at the reviewers' evaluation of these dissertations, one can easily find that only one out of the 15 showed complete performance and was valuable in all criteria. Meanwhile, the others showed strength in the first and second dimensions of the design criteria. However, their performance in the other parameters deteriorated greatly. In total, seven out of them performed moderately in design criteria (i.e. they achieved in dimensions, 1, 2 and 6, whereas they failed in the other 3, 4 and 5); as the other seven researchers performed in four dimensions moderately. Concerning the conduct criteria, they did very well. Therefore, ten out of the fifteen researchers fulfilled perfectly in all dimensions, however, only five performed somehow moderately in only four out of the five dimensions in the conduct criteria. Additionally, seven out of the fifteen achieved in all dimensions in data abstraction and analysis, whereas three contented in only four dimensions, meanwhile other three of them fulfilled only three, while the other two achieved two dimensions. Although researchers did very well in design, conduct, and data abstraction and analysis criterion, they seemed very weak in structuring and writing the review. They only achieved in the fourth and fifth dimensions of this criteria. However, they got zero achievements in the first dimension. Additionally, only six out of the fifteen researchers fulfilled the third dimension, whereas only five achieved the second one.

Findings and discussion

As mentioned above, the purpose of this study is to find out the common types of literature review used by Saudi EFL postgraduate students in Al-Baha University; and to find out the accuracy of citing information related to the topics in question; as well as to assess the quality of the literature review written by selected researchers. From the analysis, it was found that most researchers (11 out of 15) used a systematic review of the literature. Systematic reviews are the thorough and openly transparent type of literature review. Moreover, the most reliable and comprehensive statement about what works is that systematic reviews embark on identification, synthesis and assessment of the available proof, or qualitative and/or quantitative, as a way of generating a well-researched, and empirically derived answer to a specified research question (Petrosino et al. , cited in van der Knaap, 2008 ). The analysis also showed that most researchers utilized paraphrasing in their citing information. Even though it eases work for the researcher, paraphrasing may poorly present information if not used well. As advised, it is better to understand the readings and put them in your own words to preserve the accuracy of the information. Thus, understanding information and then properly paraphrasing will make the work look more original and refined. In this study, the researchers in many parts of the research failed to do an accurate performance in paraphrasing (i.e. there is an apparent weakness in meaning between the original source and the paraphrased text). This demonstrated that there was no accuracy in the paraphrasing used to cite information on the topics in question.

Regarding the quality of the literature review written by selected researchers, the data were gathered using a checklist by the evaluators who voluntarily distributed it into the inquiry to help the researcher to rate the performance of the 15 MA students in their dissertations. Generally, the results showed that students (the MA researchers) were keen on the conduct phase and then to some extent on data abstraction and analysis. Therefore, they know how to conduct their research, especially they have proper measures to ensure quality data abstraction. Moreover, chose data analysis techniques appropriately concerning the overall research questions and the data abstracted. Thus, they accurately search the process for types of reviews, and they did the inclusion and exclusion processes of articles transparent which makes their sample appropriate and in concordance with the overall purpose of the review. Additionally, in the design, concerning the relationship to the overall research field, their literature review was needed, and it makes a substantial, practical and theoretical contribution; the motivation, the purpose and the research questions were clearly stated and motivated; the methodology and the search strategy were clearly and transparently described. On the other hand, they were weak in phase 1 (design), item 3 “Does the review account for the previous literature review and other relevant literature ?”, and they did not clearly state the approaches for the literature review. Finally, the study found that they showed a weak achievement in structuring and writing the review, especially they did not organize articles coherently about the overall approach and research question, and the overall method of conducting the literature review was not sufficiently described, thus their studies could not be replicated.

Therefore, as shown in the purpose of this research, the review of intellectual production is most often the introduction to various theses or peer-review research articles, before presenting the methods and results, and its use is common in most academic research. Thus, the literature review represents one of the important parts of the scientific research plan ( Baumeister and Leary, 1997 ; Torraco, 2005 ). It is the second part that is related to the theoretical framework of the presented research methodology. Meanwhile, it is directly and closely related to the topic. Additionally, it represents an information-rich ground for those who have the desire to know all aspects of the problem or hypothesis in question. It consumes time and requires strong analytical skills from the researchers to make a great contribution successfully as mentioned by other scholars ( Boyd and Solarino, 2016 ; Mazumdar et al. , 2005 , pp. 84–102; Rodell et al ., 2016 ). As in the study questions, and to rationalize the topic, the findings concluded in this paper showed that the analysis and criticism of the literature review may require personal experiences, and others depend on the methodological foundations. The analysis and the criticism should include various dimensions (content, methodology, the sample, reliability and results). This was evident in the performance of these students in analyzing, criticizing and citing the previous studies they refer to. Thus, a researcher should have appropriate insight and wisdom to comment on previous studies and critique them constructively through compelling scientific evidence as well as to be objective and distant from any internal ideologies or personal bias. Therefore, some ideas and techniques that contribute to the process of editing, analyzing and criticizing literature review must be known by researchers ( MacInnis, 2011 ). Additionally, more attention should be given to structuring and writing the review mainly the organization of the review in relation to the overall approach and research questions.

Implications

The study came up with some implications that can help researchers in conducting their studies skillfully. These implications were drawn from the study's findings which may be very important for practice or conducting a literature review.

First: How to criticize the literature?

When looking at the literature review, one should focus on five main points that a study can follow. They are (1) content, (2) methodology, (3) the study sample, (4) credibility and (5) results. Content criticism: in this case, the researcher must express his/her point of view that the content of the previous studies does not include the technical framework that must be followed, and in that case, the study loses the advantage of comprehensiveness and moves away from objectivity in the way it is refuted.

Criticism related to methodology

Here, the researcher must clarify the negative and positive points in the scientific method followed in previous studies, and it is not a requirement that the literature might be negative or positive in its entirety. Accordingly, this is subject to the researcher's opinion, which is an expression of his/her point of view, and he/she has to present this according to convincing evidence which varies from one researcher to another.

Criticism related to the study sample

The researcher must mention any deficiencies in the sample under study which may be ineffective in judging previous literature, and it was possible to increase the sample size. To clarify a matter related to the research problem, the sample may not be represented in an appropriate statistical way, etc.

Credibility criticism

The researcher must verify the reliability of previous studies, and the method of ascertaining. This differs according to the methodology followed by the review studies (i.e. there is the descriptive, experimental and historical approach. For example, the historical method is distinguished by its credibility from others, and the researcher must refute that matter and follow the precise criteria in judging that, etc.). To judge the reliability of literature, the researcher must be familiar with all scientific research methods, their advantages and disadvantages, and the research hypotheses and theories that are compatible with those approaches.

Results criticism

The researcher may disagree with the results shown in previous studies. Because there is an error in the method of analyzing and presenting the data, so, the researcher must clarify the comparison between his/her findings and what was presented in other studies and indicate the extent of objectivity in each of them ( Snyder et al ., 2016 ; Verlegh and Steenkamp, 1999 ; Witell et al. , 2016 ). Additionally, the researcher should address only the previous studies related to the research topic, and the link must be clear to the reader, so it makes no sense to refer to previous research or studies that do not touch the research problem from near or far.

Second: How to comment on literature?

Previous studies help clarify the theoretical foundations of the subject of the research to be carried out by the researcher.

They save time and effort for the researcher by choosing the framework for the topic of the research plan.

They are a wake-up call for the researcher when writing a paper by defining a method that would avoid the researcher making mistakes made by previous researchers.

Present the correct methodological approach to the topic of research in general.

They give the researcher an exemplary method to extract recommendations, findings and other proposals related to the research.

Literature helps the researcher in identifying references for his/her research and facilitates the process of writing.

They have an important role in the researcher's comparison process between the research he provides and those studies and sources.

As many EFL MA researchers find it difficult to choose and handle a suitable literature review that approves their writing quality, thus, this study was conducted to find out a suitable step-by-step approach that can help to undertake a valid, comprehensive and helpful literature review. In conclusion, EFL MA researchers need to search for the quality and trustworthiness of their reviews to build a rich and adequate literature review. As found in this paper, it is seen that most MA Saudi researchers favored using the systematic review rather than the integrative type. More or less, they try to avoid comparing the review rather than identifying and synthesizing, as it may seem a more complicated process. Obviously, reviewing any article that could be relevant to the topic is not a simple task; therefore, a different strategy must be developed and used carefully to fulfill the quality of literature review along with the topic in question. More interestingly and generally, the researcher found that a semi-systematic review method often possesses similarities to approaches used in qualitative research ( Dundar and Fleeman, 2017 ), but it can also be combined with a statistical meta-analysis approach. Due to the integrative approach liability to yield a creative collection of data, it is widely used to combine perspectives and insights from previous research. Thus, the integrative approach seems to be the best method that can be used in the field of EFL because its purpose is to compare and combine rather than cover all related topics. Additionally, as the study found that students did not accurately paraphrase/summarize appropriately from other sources, additional sessions impeding paraphrasing procedures and processes will have valuable benefits and will make students better at writing research in the future. Concerning the phases of the quality of conducting research, it is important to ensure the proper measurement that qualifies the quality of data abstraction and analysis techniques that deal with the overall research questions accurately. Furthermore, searching for proper types of reviews, article transparency and the appropriate sample should fit the purpose of the review. Finally, among the broader implications of the study, it is expected that the construction of master's programs (courses path) should be reviewed, and focus should be given to teach students the quality standards of research writing and how to analyze and critique them in a better way.

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Leveraging Large Language Models for Literature Review Tasks - A Case Study Using ChatGPT

• Conference paper
• First Online: 20 December 2023
• Cite this conference paper

• Robert Zimmermann   ORCID: orcid.org/0000-0003-1819-6542 8 ,
• Marina Staab   ORCID: orcid.org/0009-0004-3807-5734 8 ,
• Mehran Nasseri   ORCID: orcid.org/0000-0003-3562-2240 8 , 9 &
• Patrick Brandtner   ORCID: orcid.org/0000-0002-0011-3502 8 , 9  

Part of the book series: Communications in Computer and Information Science ((CCIS,volume 1935))

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• International Conference on Advanced Research in Technologies, Information, Innovation and Sustainability

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Literature reviews constitute an indispensable component of research endeavors; however, they often prove laborious and time-intensive. This study explores the potential of ChatGPT, a prominent large-scale language model, to facilitate the literature review process. By contrasting outcomes from a manual literature review with those achieved using ChatGPT, we ascertain the accuracy of ChatGPT's responses. Our findings indicate that ChatGPT aids researchers in swiftly perusing vast and heterogeneous collections of scientific publications, enabling them to extract pertinent information related to their research topic with an overall accuracy of 70%. Moreover, we demonstrate that ChatGPT offers a more economical and expeditious means of achieving this level of accuracy compared to human researchers. Nevertheless, we conclude that although ChatGPT exhibits promise in generating a rapid and cost-effective general overview of a subject, it presently falls short of generating a comprehensive literature overview requisite for scientific applications. Lastly, we propose avenues for future research to enhance the performance and utility of ChatGPT as a literature review assistant.

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Acknowledgments

This research has been funded by both the Government of Upper Austria as part of the research grant Logistikum.Retail and by the Christian Doppler Gesellschaft as part of the Josef Ressel Centre PREVAIL.

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Zimmermann, R., Staab, M., Nasseri, M., Brandtner, P. (2024). Leveraging Large Language Models for Literature Review Tasks - A Case Study Using ChatGPT. In: Guarda, T., Portela, F., Diaz-Nafria, J.M. (eds) Advanced Research in Technologies, Information, Innovation and Sustainability. ARTIIS 2023. Communications in Computer and Information Science, vol 1935. Springer, Cham. https://doi.org/10.1007/978-3-031-48858-0_25

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Organizing Your Social Sciences Research Assignments

• Annotated Bibliography
• Analyzing a Scholarly Journal Article
• Group Presentations
• Dealing with Nervousness
• Using Visual Aids
• Grading Someone Else's Paper
• Types of Structured Group Activities
• Group Project Survival Skills
• Leading a Class Discussion
• Multiple Book Review Essay
• Reviewing Collected Works
• Writing a Case Analysis Paper
• Writing a Case Study
• About Informed Consent
• Writing Field Notes
• Writing a Policy Memo
• Writing a Reflective Paper
• Writing a Research Proposal
• Generative AI and Writing
• Acknowledgments

A case study research paper examines a person, place, event, condition, phenomenon, or other type of subject of analysis in order to extrapolate  key themes and results that help predict future trends, illuminate previously hidden issues that can be applied to practice, and/or provide a means for understanding an important research problem with greater clarity. A case study research paper usually examines a single subject of analysis, but case study papers can also be designed as a comparative investigation that shows relationships between two or more subjects. The methods used to study a case can rest within a quantitative, qualitative, or mixed-method investigative paradigm.

Case Studies. Writing@CSU. Colorado State University; Mills, Albert J. , Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010 ; “What is a Case Study?” In Swanborn, Peter G. Case Study Research: What, Why and How? London: SAGE, 2010.

How to Approach Writing a Case Study Research Paper

General information about how to choose a topic to investigate can be found under the " Choosing a Research Problem " tab in the Organizing Your Social Sciences Research Paper writing guide. Review this page because it may help you identify a subject of analysis that can be investigated using a case study design.

However, identifying a case to investigate involves more than choosing the research problem . A case study encompasses a problem contextualized around the application of in-depth analysis, interpretation, and discussion, often resulting in specific recommendations for action or for improving existing conditions. As Seawright and Gerring note, practical considerations such as time and access to information can influence case selection, but these issues should not be the sole factors used in describing the methodological justification for identifying a particular case to study. Given this, selecting a case includes considering the following:

• The case represents an unusual or atypical example of a research problem that requires more in-depth analysis? Cases often represent a topic that rests on the fringes of prior investigations because the case may provide new ways of understanding the research problem. For example, if the research problem is to identify strategies to improve policies that support girl's access to secondary education in predominantly Muslim nations, you could consider using Azerbaijan as a case study rather than selecting a more obvious nation in the Middle East. Doing so may reveal important new insights into recommending how governments in other predominantly Muslim nations can formulate policies that support improved access to education for girls.
• The case provides important insight or illuminate a previously hidden problem? In-depth analysis of a case can be based on the hypothesis that the case study will reveal trends or issues that have not been exposed in prior research or will reveal new and important implications for practice. For example, anecdotal evidence may suggest drug use among homeless veterans is related to their patterns of travel throughout the day. Assuming prior studies have not looked at individual travel choices as a way to study access to illicit drug use, a case study that observes a homeless veteran could reveal how issues of personal mobility choices facilitate regular access to illicit drugs. Note that it is important to conduct a thorough literature review to ensure that your assumption about the need to reveal new insights or previously hidden problems is valid and evidence-based.
• The case challenges and offers a counter-point to prevailing assumptions? Over time, research on any given topic can fall into a trap of developing assumptions based on outdated studies that are still applied to new or changing conditions or the idea that something should simply be accepted as "common sense," even though the issue has not been thoroughly tested in current practice. A case study analysis may offer an opportunity to gather evidence that challenges prevailing assumptions about a research problem and provide a new set of recommendations applied to practice that have not been tested previously. For example, perhaps there has been a long practice among scholars to apply a particular theory in explaining the relationship between two subjects of analysis. Your case could challenge this assumption by applying an innovative theoretical framework [perhaps borrowed from another discipline] to explore whether this approach offers new ways of understanding the research problem. Taking a contrarian stance is one of the most important ways that new knowledge and understanding develops from existing literature.
• The case provides an opportunity to pursue action leading to the resolution of a problem? Another way to think about choosing a case to study is to consider how the results from investigating a particular case may result in findings that reveal ways in which to resolve an existing or emerging problem. For example, studying the case of an unforeseen incident, such as a fatal accident at a railroad crossing, can reveal hidden issues that could be applied to preventative measures that contribute to reducing the chance of accidents in the future. In this example, a case study investigating the accident could lead to a better understanding of where to strategically locate additional signals at other railroad crossings so as to better warn drivers of an approaching train, particularly when visibility is hindered by heavy rain, fog, or at night.
• The case offers a new direction in future research? A case study can be used as a tool for an exploratory investigation that highlights the need for further research about the problem. A case can be used when there are few studies that help predict an outcome or that establish a clear understanding about how best to proceed in addressing a problem. For example, after conducting a thorough literature review [very important!], you discover that little research exists showing the ways in which women contribute to promoting water conservation in rural communities of east central Africa. A case study of how women contribute to saving water in a rural village of Uganda can lay the foundation for understanding the need for more thorough research that documents how women in their roles as cooks and family caregivers think about water as a valuable resource within their community. This example of a case study could also point to the need for scholars to build new theoretical frameworks around the topic [e.g., applying feminist theories of work and family to the issue of water conservation].

Eisenhardt, Kathleen M. “Building Theories from Case Study Research.” Academy of Management Review 14 (October 1989): 532-550; Emmel, Nick. Sampling and Choosing Cases in Qualitative Research: A Realist Approach . Thousand Oaks, CA: SAGE Publications, 2013; Gerring, John. “What Is a Case Study and What Is It Good for?” American Political Science Review 98 (May 2004): 341-354; Mills, Albert J. , Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010; Seawright, Jason and John Gerring. "Case Selection Techniques in Case Study Research." Political Research Quarterly 61 (June 2008): 294-308.

Structure and Writing Style

The purpose of a paper in the social sciences designed around a case study is to thoroughly investigate a subject of analysis in order to reveal a new understanding about the research problem and, in so doing, contributing new knowledge to what is already known from previous studies. In applied social sciences disciplines [e.g., education, social work, public administration, etc.], case studies may also be used to reveal best practices, highlight key programs, or investigate interesting aspects of professional work.

In general, the structure of a case study research paper is not all that different from a standard college-level research paper. However, there are subtle differences you should be aware of. Here are the key elements to organizing and writing a case study research paper.

I.  Introduction

As with any research paper, your introduction should serve as a roadmap for your readers to ascertain the scope and purpose of your study . The introduction to a case study research paper, however, should not only describe the research problem and its significance, but you should also succinctly describe why the case is being used and how it relates to addressing the problem. The two elements should be linked. With this in mind, a good introduction answers these four questions:

• What is being studied? Describe the research problem and describe the subject of analysis [the case] you have chosen to address the problem. Explain how they are linked and what elements of the case will help to expand knowledge and understanding about the problem.
• Why is this topic important to investigate? Describe the significance of the research problem and state why a case study design and the subject of analysis that the paper is designed around is appropriate in addressing the problem.
• What did we know about this topic before I did this study? Provide background that helps lead the reader into the more in-depth literature review to follow. If applicable, summarize prior case study research applied to the research problem and why it fails to adequately address the problem. Describe why your case will be useful. If no prior case studies have been used to address the research problem, explain why you have selected this subject of analysis.
• How will this study advance new knowledge or new ways of understanding? Explain why your case study will be suitable in helping to expand knowledge and understanding about the research problem.

Each of these questions should be addressed in no more than a few paragraphs. Exceptions to this can be when you are addressing a complex research problem or subject of analysis that requires more in-depth background information.

II.  Literature Review

The literature review for a case study research paper is generally structured the same as it is for any college-level research paper. The difference, however, is that the literature review is focused on providing background information and  enabling historical interpretation of the subject of analysis in relation to the research problem the case is intended to address . This includes synthesizing studies that help to:

• Place relevant works in the context of their contribution to understanding the case study being investigated . This would involve summarizing studies that have used a similar subject of analysis to investigate the research problem. If there is literature using the same or a very similar case to study, you need to explain why duplicating past research is important [e.g., conditions have changed; prior studies were conducted long ago, etc.].
• Describe the relationship each work has to the others under consideration that informs the reader why this case is applicable . Your literature review should include a description of any works that support using the case to investigate the research problem and the underlying research questions.
• Identify new ways to interpret prior research using the case study . If applicable, review any research that has examined the research problem using a different research design. Explain how your use of a case study design may reveal new knowledge or a new perspective or that can redirect research in an important new direction.
• Resolve conflicts amongst seemingly contradictory previous studies . This refers to synthesizing any literature that points to unresolved issues of concern about the research problem and describing how the subject of analysis that forms the case study can help resolve these existing contradictions.
• Point the way in fulfilling a need for additional research . Your review should examine any literature that lays a foundation for understanding why your case study design and the subject of analysis around which you have designed your study may reveal a new way of approaching the research problem or offer a perspective that points to the need for additional research.
• Expose any gaps that exist in the literature that the case study could help to fill . Summarize any literature that not only shows how your subject of analysis contributes to understanding the research problem, but how your case contributes to a new way of understanding the problem that prior research has failed to do.
• Locate your own research within the context of existing literature [very important!] . Collectively, your literature review should always place your case study within the larger domain of prior research about the problem. The overarching purpose of reviewing pertinent literature in a case study paper is to demonstrate that you have thoroughly identified and synthesized prior studies in relation to explaining the relevance of the case in addressing the research problem.

III.  Method

In this section, you explain why you selected a particular case [i.e., subject of analysis] and the strategy you used to identify and ultimately decide that your case was appropriate in addressing the research problem. The way you describe the methods used varies depending on the type of subject of analysis that constitutes your case study.

If your subject of analysis is an incident or event . In the social and behavioral sciences, the event or incident that represents the case to be studied is usually bounded by time and place, with a clear beginning and end and with an identifiable location or position relative to its surroundings. The subject of analysis can be a rare or critical event or it can focus on a typical or regular event. The purpose of studying a rare event is to illuminate new ways of thinking about the broader research problem or to test a hypothesis. Critical incident case studies must describe the method by which you identified the event and explain the process by which you determined the validity of this case to inform broader perspectives about the research problem or to reveal new findings. However, the event does not have to be a rare or uniquely significant to support new thinking about the research problem or to challenge an existing hypothesis. For example, Walo, Bull, and Breen conducted a case study to identify and evaluate the direct and indirect economic benefits and costs of a local sports event in the City of Lismore, New South Wales, Australia. The purpose of their study was to provide new insights from measuring the impact of a typical local sports event that prior studies could not measure well because they focused on large "mega-events." Whether the event is rare or not, the methods section should include an explanation of the following characteristics of the event: a) when did it take place; b) what were the underlying circumstances leading to the event; and, c) what were the consequences of the event in relation to the research problem.

If your subject of analysis is a person. Explain why you selected this particular individual to be studied and describe what experiences they have had that provide an opportunity to advance new understandings about the research problem. Mention any background about this person which might help the reader understand the significance of their experiences that make them worthy of study. This includes describing the relationships this person has had with other people, institutions, and/or events that support using them as the subject for a case study research paper. It is particularly important to differentiate the person as the subject of analysis from others and to succinctly explain how the person relates to examining the research problem [e.g., why is one politician in a particular local election used to show an increase in voter turnout from any other candidate running in the election]. Note that these issues apply to a specific group of people used as a case study unit of analysis [e.g., a classroom of students].

If your subject of analysis is a place. In general, a case study that investigates a place suggests a subject of analysis that is unique or special in some way and that this uniqueness can be used to build new understanding or knowledge about the research problem. A case study of a place must not only describe its various attributes relevant to the research problem [e.g., physical, social, historical, cultural, economic, political], but you must state the method by which you determined that this place will illuminate new understandings about the research problem. It is also important to articulate why a particular place as the case for study is being used if similar places also exist [i.e., if you are studying patterns of homeless encampments of veterans in open spaces, explain why you are studying Echo Park in Los Angeles rather than Griffith Park?]. If applicable, describe what type of human activity involving this place makes it a good choice to study [e.g., prior research suggests Echo Park has more homeless veterans].

If your subject of analysis is a phenomenon. A phenomenon refers to a fact, occurrence, or circumstance that can be studied or observed but with the cause or explanation to be in question. In this sense, a phenomenon that forms your subject of analysis can encompass anything that can be observed or presumed to exist but is not fully understood. In the social and behavioral sciences, the case usually focuses on human interaction within a complex physical, social, economic, cultural, or political system. For example, the phenomenon could be the observation that many vehicles used by ISIS fighters are small trucks with English language advertisements on them. The research problem could be that ISIS fighters are difficult to combat because they are highly mobile. The research questions could be how and by what means are these vehicles used by ISIS being supplied to the militants and how might supply lines to these vehicles be cut off? How might knowing the suppliers of these trucks reveal larger networks of collaborators and financial support? A case study of a phenomenon most often encompasses an in-depth analysis of a cause and effect that is grounded in an interactive relationship between people and their environment in some way.

NOTE:   The choice of the case or set of cases to study cannot appear random. Evidence that supports the method by which you identified and chose your subject of analysis should clearly support investigation of the research problem and linked to key findings from your literature review. Be sure to cite any studies that helped you determine that the case you chose was appropriate for examining the problem.

IV.  Discussion

The main elements of your discussion section are generally the same as any research paper, but centered around interpreting and drawing conclusions about the key findings from your analysis of the case study. Note that a general social sciences research paper may contain a separate section to report findings. However, in a paper designed around a case study, it is common to combine a description of the results with the discussion about their implications. The objectives of your discussion section should include the following:

Reiterate the Research Problem/State the Major Findings Briefly reiterate the research problem you are investigating and explain why the subject of analysis around which you designed the case study were used. You should then describe the findings revealed from your study of the case using direct, declarative, and succinct proclamation of the study results. Highlight any findings that were unexpected or especially profound.

Explain the Meaning of the Findings and Why They are Important Systematically explain the meaning of your case study findings and why you believe they are important. Begin this part of the section by repeating what you consider to be your most important or surprising finding first, then systematically review each finding. Be sure to thoroughly extrapolate what your analysis of the case can tell the reader about situations or conditions beyond the actual case that was studied while, at the same time, being careful not to misconstrue or conflate a finding that undermines the external validity of your conclusions.

Relate the Findings to Similar Studies No study in the social sciences is so novel or possesses such a restricted focus that it has absolutely no relation to previously published research. The discussion section should relate your case study results to those found in other studies, particularly if questions raised from prior studies served as the motivation for choosing your subject of analysis. This is important because comparing and contrasting the findings of other studies helps support the overall importance of your results and it highlights how and in what ways your case study design and the subject of analysis differs from prior research about the topic.

Consider Alternative Explanations of the Findings Remember that the purpose of social science research is to discover and not to prove. When writing the discussion section, you should carefully consider all possible explanations revealed by the case study results, rather than just those that fit your hypothesis or prior assumptions and biases. Be alert to what the in-depth analysis of the case may reveal about the research problem, including offering a contrarian perspective to what scholars have stated in prior research if that is how the findings can be interpreted from your case.

Acknowledge the Study's Limitations You can state the study's limitations in the conclusion section of your paper but describing the limitations of your subject of analysis in the discussion section provides an opportunity to identify the limitations and explain why they are not significant. This part of the discussion section should also note any unanswered questions or issues your case study could not address. More detailed information about how to document any limitations to your research can be found here .

Suggest Areas for Further Research Although your case study may offer important insights about the research problem, there are likely additional questions related to the problem that remain unanswered or findings that unexpectedly revealed themselves as a result of your in-depth analysis of the case. Be sure that the recommendations for further research are linked to the research problem and that you explain why your recommendations are valid in other contexts and based on the original assumptions of your study.

V.  Conclusion

As with any research paper, you should summarize your conclusion in clear, simple language; emphasize how the findings from your case study differs from or supports prior research and why. Do not simply reiterate the discussion section. Provide a synthesis of key findings presented in the paper to show how these converge to address the research problem. If you haven't already done so in the discussion section, be sure to document the limitations of your case study and any need for further research.

The function of your paper's conclusion is to: 1) reiterate the main argument supported by the findings from your case study; 2) state clearly the context, background, and necessity of pursuing the research problem using a case study design in relation to an issue, controversy, or a gap found from reviewing the literature; and, 3) provide a place to persuasively and succinctly restate the significance of your research problem, given that the reader has now been presented with in-depth information about the topic.

Consider the following points to help ensure your conclusion is appropriate:

• If the argument or purpose of your paper is complex, you may need to summarize these points for your reader.
• If prior to your conclusion, you have not yet explained the significance of your findings or if you are proceeding inductively, use the conclusion of your paper to describe your main points and explain their significance.
• Move from a detailed to a general level of consideration of the case study's findings that returns the topic to the context provided by the introduction or within a new context that emerges from your case study findings.

Note that, depending on the discipline you are writing in or the preferences of your professor, the concluding paragraph may contain your final reflections on the evidence presented as it applies to practice or on the essay's central research problem. However, the nature of being introspective about the subject of analysis you have investigated will depend on whether you are explicitly asked to express your observations in this way.

Problems to Avoid

Overgeneralization One of the goals of a case study is to lay a foundation for understanding broader trends and issues applied to similar circumstances. However, be careful when drawing conclusions from your case study. They must be evidence-based and grounded in the results of the study; otherwise, it is merely speculation. Looking at a prior example, it would be incorrect to state that a factor in improving girls access to education in Azerbaijan and the policy implications this may have for improving access in other Muslim nations is due to girls access to social media if there is no documentary evidence from your case study to indicate this. There may be anecdotal evidence that retention rates were better for girls who were engaged with social media, but this observation would only point to the need for further research and would not be a definitive finding if this was not a part of your original research agenda.

Failure to Document Limitations No case is going to reveal all that needs to be understood about a research problem. Therefore, just as you have to clearly state the limitations of a general research study , you must describe the specific limitations inherent in the subject of analysis. For example, the case of studying how women conceptualize the need for water conservation in a village in Uganda could have limited application in other cultural contexts or in areas where fresh water from rivers or lakes is plentiful and, therefore, conservation is understood more in terms of managing access rather than preserving access to a scarce resource.

Failure to Extrapolate All Possible Implications Just as you don't want to over-generalize from your case study findings, you also have to be thorough in the consideration of all possible outcomes or recommendations derived from your findings. If you do not, your reader may question the validity of your analysis, particularly if you failed to document an obvious outcome from your case study research. For example, in the case of studying the accident at the railroad crossing to evaluate where and what types of warning signals should be located, you failed to take into consideration speed limit signage as well as warning signals. When designing your case study, be sure you have thoroughly addressed all aspects of the problem and do not leave gaps in your analysis that leave the reader questioning the results.

Case Studies. Writing@CSU. Colorado State University; Gerring, John. Case Study Research: Principles and Practices . New York: Cambridge University Press, 2007; Merriam, Sharan B. Qualitative Research and Case Study Applications in Education . Rev. ed. San Francisco, CA: Jossey-Bass, 1998; Miller, Lisa L. “The Use of Case Studies in Law and Social Science Research.” Annual Review of Law and Social Science 14 (2018): TBD; Mills, Albert J., Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010; Putney, LeAnn Grogan. "Case Study." In Encyclopedia of Research Design , Neil J. Salkind, editor. (Thousand Oaks, CA: SAGE Publications, 2010), pp. 116-120; Simons, Helen. Case Study Research in Practice . London: SAGE Publications, 2009;  Kratochwill,  Thomas R. and Joel R. Levin, editors. Single-Case Research Design and Analysis: New Development for Psychology and Education .  Hilldsale, NJ: Lawrence Erlbaum Associates, 1992; Swanborn, Peter G. Case Study Research: What, Why and How? London : SAGE, 2010; Yin, Robert K. Case Study Research: Design and Methods . 6th edition. Los Angeles, CA, SAGE Publications, 2014; Walo, Maree, Adrian Bull, and Helen Breen. “Achieving Economic Benefits at Local Events: A Case Study of a Local Sports Event.” Festival Management and Event Tourism 4 (1996): 95-106.

Writing Tip

At Least Five Misconceptions about Case Study Research

Social science case studies are often perceived as limited in their ability to create new knowledge because they are not randomly selected and findings cannot be generalized to larger populations. Flyvbjerg examines five misunderstandings about case study research and systematically "corrects" each one. To quote, these are:

Misunderstanding 1 :  General, theoretical [context-independent] knowledge is more valuable than concrete, practical [context-dependent] knowledge. Misunderstanding 2 :  One cannot generalize on the basis of an individual case; therefore, the case study cannot contribute to scientific development. Misunderstanding 3 :  The case study is most useful for generating hypotheses; that is, in the first stage of a total research process, whereas other methods are more suitable for hypotheses testing and theory building. Misunderstanding 4 :  The case study contains a bias toward verification, that is, a tendency to confirm the researcher’s preconceived notions. Misunderstanding 5 :  It is often difficult to summarize and develop general propositions and theories on the basis of specific case studies [p. 221].

While writing your paper, think introspectively about how you addressed these misconceptions because to do so can help you strengthen the validity and reliability of your research by clarifying issues of case selection, the testing and challenging of existing assumptions, the interpretation of key findings, and the summation of case outcomes. Think of a case study research paper as a complete, in-depth narrative about the specific properties and key characteristics of your subject of analysis applied to the research problem.

Flyvbjerg, Bent. “Five Misunderstandings About Case-Study Research.” Qualitative Inquiry 12 (April 2006): 219-245.

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Associations between transport modes and site-specific cancers: a systematic review and meta-analysis

• Win Thu 1 ,
• Alistair Woodward 1 ,
• Alana Cavadino 1 &
• Sandar Tin Tin 1 , 2  

Environmental Health volume  23 , Article number:  39 ( 2024 ) Cite this article

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Physical inactivity is a global public health problem. A practical solution would be to build physical activity into the daily routine by using active modes of transport. Choice of transport mode can influence cancer risk through their effects on levels of physical activity, sedentary time, and environmental pollution. This review synthesizes existing evidence on the associations of specific transport modes with risks of site-specific cancers.

Relevant literature was searched in PubMed, Embase, and Scopus from 1914 to 17th February 2023. For cancer sites with effect measures available for a specific transport mode from two or more studies, random effects meta-analyses were performed to pool relative risks (RR) comparing the highest vs. lowest activity group as well as per 10 Metabolic Equivalent of Task (MET) hour increment in transport-related physical activity per week ( ∼ 150 min of walking or 90 min of cycling).

27 eligible studies (11 cohort, 15 case-control, and 1 case-cohort) were identified, which reported the associations of transport modes with 10 site-specific cancers. In the meta-analysis, 10 MET hour increment in transport-related physical activity per week was associated with a reduction in risk for endometrial cancer (RR: 0.91, 95% CI: 0.83–0.997), colorectal cancer (RR: 0.95, 95% CI: 0.91–0.99) and breast cancer (RR: 0.99, 95% CI: 0.89–0.996). The highest level of walking only or walking and cycling combined modes, compared to the lowest level, were significantly associated with a 12% and 30% reduced risk of breast and endometrial cancers respectively. Cycling, compared to motorized modes, was associated with a lower risk of overall cancer incidence and mortality.

Active transport appears to reduce cancer risk, but evidence for cancer sites other than colorectum, breast, and endometrium is currently limited.

Peer Review reports

Introduction

Physical inactivity is a global public health problem, contributing to substantial disease and economic burden worldwide [ 1 , 2 ]. With rapid changes in technology, lifestyle, and habitual environment, people have been less active and more sedentary over the past few decades. Globally, about 1 in 4 adults were not active, i.e., did not meet the World Health Organization (WHO) recommendation of engaging at least 150–300 min of moderate-intensity or 75–150 min of vigorous-intensity aerobic physical activity per week [ 3 ], but the prevalence varied widely within and across countries [ 4 ]. If the current trends continue, it is unlikely that the WHO’s target to reduce physical inactivity by 10% in 2025 will be met.

One practical solution would be to build physical activity into the daily routine by using active modes of transport [ 5 ]. Walking and cycling have been shown to improve health (mainly all-cause mortality, cardiovascular disease, diabetes, and cancer) [ 6 ] and also provide social, economic and environmental benefits [ 7 , 8 ]. Car use, on the other hand, contributes to a significant proportion of daily sedentary time, and the situation is worsening with increasing traffic congestion/delays [ 9 ]; it has been associated with an increased risk of obesity and related outcomes [ 10 ]. Further, exposure to environmental pollutants such as nitrogen dioxide and/or particulate matter could differ across different road users [ 11 ], while it has been shown to increase the risk of certain cancers, particularly lung cancer [ 12 ].

While there is ample evidence linking leisure time physical activity or physical activity in general with a reduced risk for a number of cancer sites [ 13 , 14 ], and sedentary behavior in general with an increased risk [ 15 ], the findings may not be directly applicable to transport-related activity because the context and correlates of activity as well as its frequency, duration and intensity are likely to be different across different domains. We therefore reviewed the existing literature that reported the associations between transport modes and risks of site-specific cancers.

A systematic literature review and meta-analysis was conducted and reported according to the PRISMA guideline (Supplementary file S1 ). The review was not registered.

Search strategy and study selection

Relevant literature was searched from 1914 to 17th February 2023 in PubMed, Scopus, and Embase databases using the relevant search terms such as walking, cycling, car, public transport, commute and cancers. Site-specific cancers known to be associated with physical activity and body weight such as breast, colon, liver, esophageal adenocarcinoma and those associated with environmental factor such as lung and melanoma of skin were also searched (Supplementary file S2 ). The reference lists of systematic reviews on physical activity and cancers were also reviewed. Studies were included if they (1) used cohort, case-control, case-cohort or experimental design, (2) assessed transport modes such as walking, cycling, public transport or car use as the exposures of interest, (3) investigated one or more site-specific cancers, overall cancer incidence and/or mortality as the outcome(s), (4) reported effect measures associated with transport modes, and (5) published the full article in English. Studies that used cross-sectional design or mathematical modeling to estimate health impacts at the population level were excluded. Details of excluded studies after full text review, together with the reasons for exclusion, were provided in the Supplementary file S3 . WT conducted the search and selection, and STT oversaw the process.

Data extraction and study quality assessment

Information about title, first author, year of publication, study name (if available), country, study design, sample size, age range of the participants, follow-up duration (for cohort and case-cohort studies), data collection tool, measurement units for exposure(s), data sources for outcome(s), site-specific cancer assessed, effect measures, and confounders adjusted were extracted in a standardized data collection spreadsheet. The study quality was evaluated using the Newcastle-Ottawa Scale (NOS) [ 16 ], which scores the cohort and case-control studies based on three domains: selection of study groups, comparability of the groups and ascertainment of exposure (case-control studies) or outcome (cohort studies). For the second domain, a point was awarded for adjustment of Body Mass Index (BMI) - to evaluate the direct vs. indirect (through BMI) effect of physical activity on cancer risk, and another point for adjustment of physical activities from other domains - to isolate the effects of transport-related physical activity from other activities. A maximum of nine points were awarded, with a higher score indicating better quality [ 16 ]. For case-cohort studies, the NOS scale for cohort studies was used. WT conducted the data extraction and quality assessment, and STT oversaw the process.

Data analysis

For cancer sites with effect measures available for a specific transport mode from two or more studies, meta-analyses were performed using random effects models. The analyses compared the highest level of active transport such as walking, cycling or mixed mode with the lowest level as reported in the individual studies. Where necessary, the reference category for exposure was changed to the lowest group to facilitate pooling of the risks [ 17 ]. The pooled relative risks (RRs) and 95% CI were presented for breast, endometrial, colorectal and testicular cancers, and overall cancer mortality.

For studies that reported time or MET as measurement units, the dose-response effects were estimated using the trend estimation method proposed by Greenland and Longnecker [ 18 ]. The reported time spent for each mode/category was converted to MET hours (see Supplementary file S4 for conversion values and formulas used). For studies that only reported estimates for categorical exposures, study-specific slopes were calculated from the natural logs of the reported risk estimates across categories and risk estimates per unit change were then estimated. The pooled results were presented per 10 Metabolic Equivalent of Task (MET) hour increment in transport-related physical activity per week ( ∼ 150 min of walking or 90 min of cycling) to align with the WHO’s physical activity recommendation [ 3 ]. This approach enabled us to pool risk estimates from a large number of studies irrespective of how the exposures were assessed (e.g., walking and cycling separately or combined) or categorised. The results were presented for breast, endometrial, colorectal, prostate cancers, and overall cancer mortality.

Meta-analysis was not conducted for the studies that compared active and non-active modes in relation to overall cancer incidence and mortality due to the potential overlap of the study samples.

For meta-analyses involving four or more studies, publication bias was assessed through the visual inspection of funnel plots, Begg’s rank correlation test, and Egger’s regression test for asymmetry. If significant associations were observed, sensitivity analyses were conducted by removing one study at a time from the initial meta-analysis to test the robustness of the results. Where possible, sub-group analyses were performed to assess variability of summary effects across population groups (Western vs. Asian), study design (cohort vs. case-control), measurement units (time vs. MET) and adjustment for BMI (yes vs. no). Metafor [ 19 ] and dosresmeta [ 20 ] R packages were used for meta-analysis and trend estimation. All authors have access to the data.

Of the 11,829 records identified, 27 unique studies (total 34 publications) were included, of which 22 studies (28 records) contributed to the meta-analyses (Fig.  1 ). There were four publications from the Netherlands Cohort Study which reported endometrial [ 21 ], ovarian [ 22 ], prostate [ 23 ], and colorectal [ 24 ] cancers, three publications from United Kingdom Biobank which reported lung [ 25 ], breast and colon [ 26 ], and overall cancer incidence and mortality [ 27 ], two publications from Shanghai Women’s Health Study which reported breast [ 28 ] and overall cancer mortality [ 29 ], and two publications from National Institutes of Health - American Association of Retired Persons Diet and Health Study which reported breast [ 30 ] and endometrial [ 31 ] cancers. Of the included studies, 20 compared the risks between the highest and lowest levels of active transport (e.g., walking, cycling, walking and cycling) and two compared the risk between active and non-active commuting modes. The majority used case-control design ( n  = 15), followed by cohort ( n  = 11) and case-cohort ( n  = 1) designs. Most of the studies were conducted in North America, mainly in the United States (US) ( n  = 7), followed by Europe ( n  = 5), China ( n  = 5), United Kingdom ( n  = 4), Australia ( n  = 2) and the remaining four studies were from India, Iran, Brazil and Nigeria. (Table  1 )

Almost half of the studies assessed walking and cycling combined, i.e., did not provide the risk estimates for each mode ( n  = 13), while others assessed walking and cycling separately ( n  = 8), or assessed only one mode (walking: n  = 3 and cycling: n  = 3). Most studies quantified active transport in terms of time spent (e.g., minutes per day, hours per week) ( n  = 14) or MET ( n  = 7), but others assessed it in terms of activity status (e.g., yes, no) ( n  = 3), or in comparison to car or motorized mode ( n  = 2), and distance ( n  = 1) (Supplementary file S5 ). The studies reported the risks associated with ten site-specific cancers, most commonly breast ( n  = 12), endometrial ( n  = 5), and colorectal ( n  = 4) cancers (Fig.  2 ). Cancer cases were identified through cancer registries, death registries, pathological reports, or hospital or medical records (Supplementary file S5 ). The NOS score for cohort studies ranged from 5 to 9, with an average score of 6.5, and the score for case-control studies ranged from 4 to 7, with an average score of 5.6 (Table  1 , detailed scoring in Supplementary file S6 , S7 ).

Flow diagram for study selection

Cancers reported in the studies

Active transport studies

The pooled results were presented for breast, endometrial, colorectal, testicular and prostate cancers, and overall cancer mortality (Fig.  3 ). For other cancers where only one study was identified, the results from the individual study were presented.

Breast cancer

In the meta-analysis of six studies comparing the highest vs. lowest activity group, an inverse association was observed for walking (RR: 0.88, 95% CI: 0.78–0.98), a borderline inverse association for cycling (RR: 0.90, 95% CI: 0.77–1.05) and no significant association for walking and cycling combined (RR: 0.97, 95% CI: 0.84–1.12). 10 MET hour increment in transport-related physical activity per week ( ∼ 150 min of walking or 90 min of cycling) was associated with a marginally reduced risk (RR: 0.99, 95% CI: 0.97–0.996). (Fig. 3 , detailed forest plots in the supplementary file S9 )

Endometrial cancer

The meta-analysis of four studies indicated that walking and cycling combined was associated with a reduced risk of endometrial cancer (RR comparing highest vs. lowest: 0.70, 95% CI: 0.56–0.87; RR per 10 MET hour increment in activity per week: 0.91, 95% CI: 0.83–0.997). (Fig.  3 , detailed forest plots in S9 )

Colorectal cancer

In the meta-analysis of two studies, walking and cycling combined was associated with a reduced risk of colorectal cancer (RR comparing highest vs. lowest: 0.89, 95% CI: 0.78–1.01; RR per 10 MET hour increment in activity per week: 0.95, 95% CI: 0.91–0.99) (Fig.  3 , detailed forest plot in S9 ).

Testicular cancer

In the meta-analysis of two studies, there was no significant association between cycle commuting in adolescence and testicular germ cell cancer (RR comparing highest vs. lowest: 1.23, 95% CI: 0.71–2.13). (Fig.  3 , detailed forest plot in S9 )

Prostate cancer

10 MET hour increment per week for transport related physical activity was associated with a reduced risk of prostate cancer (RR: 0.96, 95% CI: 0.88–1.04) (Fig.  3 , detailed forest plot in S9 ).

Ovarian cancer

Only a case-cohort study assessed the relationship of walking and cycling combined mode with ovarian cancer risk, and reported no significant association (Supplementary file S5 ) [ 22 ].

Liver, gallbladder and biliary tract cancers

A cohort study reported a significant association of commuting physical activity with a reduced risk of gallbladder and biliary tract cancers in women (HR: 0.51, 95% CI: 0.28–0.94) but not in men (HR: 0.92, 95% CI: 0.61–1.37); there was no significant association with liver cancer in both sexes (supplementary file S5 ) [ 49 ].

Renal cancer

A case-control study assessed the association of walking and cycling with risk of renal cell carcinoma in white and black participants in the ages of 20s and 50s, and reported a significant association in the white participants in their 20s (OR comparing lowest vs. highest: 1.42, 95% CI: 1.10–1.83) but not in the black counterparts; the associations were also not significant in both groups in their 50s. (Supplementary file S5 ) [ 50 ].

Overall cancer mortality

In the meta-analyses of two studies, there was an inverse association for cycling only (RR comparing highest vs. lowest: 0.60, 95% CI: 0.34–1.04) and walking and cycling combined (RR: 0.98, 95% CI: 0.86–1.12), and also per 10 MET hour increment in activity per week (RR: 0.97, 95% CI: 0.92–1.01). (Fig.  3 , detailed forest plots in S9 )

In sub-group analyses, similar associations were observed between walking and breast cancer risk in terms of study design (cohort, case-control), population (western vs. Asian), measurement unit (time vs. MET), menopausal status (premenopausal and postmenopausal) and adjustment of BMI (yes vs. no); however, the associations were stronger in studies that adjusted for physical activity from other domains (Supplementary file S10 ). In the leave-one-out analyses assessing walking and breast cancer risk, the results were sensitive to effect sizes from some studies, but this was not the case for walking and cycling combined mode and endometrial cancer (Supplementary file S11 ). There was no evidence for funnel plot asymmetry; Egger’s regression tests and Begg’s ranks correlation tests were not significant (Supplementary file S12 ).

Results of meta-analysis for active transport studies. RE = a random-effects model, MET = Metabolic Equivalent of Task, I 2  = I 2 statistics for heterogeneity, RR = Summary relative risk

Studies comparing active vs. non-active modes for commuting

Four eligible publications were identified, of which three used the data from UK Biobank [ 25 , 26 , 27 ], one used the UK census data [ 51 ]. Three reported the associations for overall cancer incidence and mortality, and one reported the risk associated with lung cancer (Fig.  4 ). In the study that assessed lung cancer using the data from UK Biobank, when compared to automobile only mode, active modes did not show a significant association whereas frequent use of public transport (≥ 5 trips per week) was associated with an increased risk of lung cancer (HR: 1.58, 95% CI: 1.08–2.33) [ 25 ] (Fig.  4 ). In another UK Biobank study, no significant associations were observed for breast and colon cancers, and overall cancer incidence and mortality when more active patterns of commuting (walking, cycling, public transport, either alone or in combination with car) were compared to car only mode [ 26 ].

The results of two studies [ 27 , 51 ] that assessed overall cancer incidence and mortality were not combined as the outcome data was extracted from the same national cancer registry with an overlapped time frame (1991–2011 and 2007–2014), although the exposure information came from different sources (census and UK Biobank). In these studies, compared to private motorized mode or non-active mode, cycling was inversely associated with overall cancer incidence and mortality. Walking and public transport were also inversely associated with overall cancer incidence in the study that used the census data [ 51 ].

Results of the individual studies comparing active vs. non-active modes for commuting. Private motorized mode = car or motorcycle, Non-active = car or public transport, Active patterns of commuting = any other patterns including walking, cycling, public transport, either alone or in combination with car, HR = Hazard Ratio, regular:1–4, often: ≥5 work-bound trips/week

This review identified 27 studies (34 publications) that reported the associations of specific transport modes, mainly active transport modes, with risks of ten site-specific cancers along with overall cancer incidence and mortality. The most frequently studied cancer sites were breast, endometrium, and colorectum; our meta-analysis showed a reduction in risk of these cancers (1%, 9% and 5%, respectively) per 10 MET hour per week increment in transport-related physical activity ( ∼ 150 min of walking or 90 min of cycling).

We found an inverse association between active transport and risks of breast and endometrial cancers, with similar magnitude of risk reduction observed in previous systematic reviews on physical activity in general [ 55 , 56 ]. While obesity is known to increase post-menopausal but not pre-menopausal breast cancer risk [ 57 ], we found similar results by menopausal status. In contrast, an earlier review did not find any significant association between walking in general and risk of pre- or post-menopausal breast cancer [ 58 ], possibly because compared to walking for transport, walking for leisure or at home generally uses lower energy [ 59 ], and therefore may have less effect on body weight.

The inverse association of active transport with colorectal cancer risk observed in this review is also consistent with the findings from existing reviews on transport-related physical activity [ 60 ] as well as physical activity in general [ 61 ]. While physical activity in general or for leisure has also been associated with a reduced risk of many other cancer sites including liver, gastric, renal and lung [ 13 , 14 ], the evidence related to transport-related physical activity is currently limited.

Mechanisms linking physical activity with specific cancer sites have been proposed, including its effects on sex hormones (breast, endometrial and prostate cancers), insulin sensitivity, glucose metabolism and adipokines (obesity-related cancers), and inflammation and immune function (most cancers) [ 62 ]. For colorectal cancer, another potential mechanism is reduced contact time between carcinogens and bowel mucosa cells due to exercise-induced intestinal mobility [ 63 ].

The overall quality of the included studies, evaluated by NOS score, ranged from 4 to 9, and in general, cohort studies tend to have higher scores compared to case-control studies. The common criteria the studies did not meet include: inadequate exposure assessment, loss to follow-up (cohort studies) and low response rates (case-control studies). While we were not able to undertake subgroup analyses by NOS score due to the limited number of studies available, our subgroup analyses by study design showed similar associations between walking and breast cancer in cohort vs. case-control studies.

To our knowledge, this review represents the first systematic attempt to synthesize the existing evidence on specific transport modes and site-specific cancers. We provided mode-specific summary effects where possible and calculated the dose-response effects for transport-related physical activity, in line with WHO physical activity recommendation. When interpreting the findings, some limitations need to be considered. First, the review may not have included some eligible studies published in languages other than English. Second, due to the limited number of available studies, we were not able to pool the results separately for cohort and case-control studies; however, we conducted sub-group analyses by study design where possible. We were not able to evaluate the non-linear relationship between transport-related physical activity and the risks of site-specific cancers. While a recent systematic review on breast and colon cancers reported a linear relationship with physical activity [ 64 ], others suggested a non-linear relationship between physical activity and cancer risk [ 65 , 66 ]. Further, variations in measurement and categorization of the exposure across the studies make direct comparison of the results between different modes (e.g., walking vs. cycling) difficult. Finally, the majority of the studies included were conducted in high income countries in Europe, UK, and North America, limiting the generalizability of the findings to other populations and low and middle income countries where urbanization and motorization are mainly taking place [ 67 ].

Our findings suggest that transport choices may influence cancer risk, particularly of obesity-related cancers such as breast, colon and endometrial cancers. Breast cancer is the most common cancer in women globally, with an estimated over 2 million new cases (11.7% of all new cases) in 2020, while colon cancer stood at fourth place (over 1 million cases, 6% of total cases) [ 68 ]. The incidence of endometrial cancer also seems to be increasing in many countries particularly in younger women. Our findings indicate that the risks of these cancers can be reduced by meeting the WHO physical activity recommendation through active commuting ( ∼ 150 min of walking or 90 min of cycling per week). Yet, the current evidence is limited in relation to other cancer sites, underlying mechanisms, and potential environmental influences, requiring further exploration.

Given heterogeneity in exposure measurements in the existing studies, harmonizing choice of the assessment tool (e.g., using International Physical Activity Questionnaires that can capture information about all four physical activity domains including transport modes), and reporting the dose-response estimates for each transport mode such as walking and cycling separately rather than a combined mode would enhance comparability of results and provide mode-specific effects. Repeated or regular assessments of exposures/transport modes used throughout the study duration would capture changes and their potential impact on outcomes in cohort studies. Importantly, more research is needed in low and middle-income settings to generate context-specific evidence.

In conclusion, active transport modes appear to reduce cancer risk, but evidence for cancer sites other than colorectum, breast and endometrium is currently limited.

Data availability

No datasets were generated or analysed during the current study.

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Acknowledgements

STT is supported by Sir Charles Hercus Health Research Fellowship from the Health Research Council of New Zealand (Ref: 23/051).

STT is supported by Sir Charles Hercus Health Research Fellowship from the Health Research Council of New Zealand (Ref: 23/051). The funder had no role in the study design, data collection, data analysis, data interpretation, writing of the report, approval of the manuscript, or decision to submit the manuscript for publication.

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STT, AW, WT designed the study. STT supervised the study. WT conducted literature search, data analysis and wrote the original draft with critical inputs from STT, AC, and AW. All authors had full access to all the data in the study and had final responsibility for the decision to submit for publication. More than one author has directly accessed and verified the underlying data reported in the manuscript.

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: Supplementary file S1 PRISMA checklist. Supplementary file S2 Literature search strategy. Supplementary file S3 List of excluded full texts with reasons. Supplementary file S4 Metabolic Equivalent of Task (MET) values used and MET hour per week conversion formulas. Supplementary file S5 Measurement units, effect measures and covariates included in the studies. Supplementary file S6 Newcastle-Ottawa Score of the studies (cohort studies). Supplementary file S7 Newcastle-Ottawa Score of the studies (case control studies). Supplementary file S8 Risks estimates used in the meta-analyses (separate excel sheet). Supplementary file S9 Forest plots. Supplementary file S10 Sub-group and covariates adjustment analyses. Supplementary file S11 Sensitivity analysis. Supplementary file S12 Funnel plots

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Thu, W., Woodward, A., Cavadino, A. et al. Associations between transport modes and site-specific cancers: a systematic review and meta-analysis. Environ Health 23 , 39 (2024). https://doi.org/10.1186/s12940-024-01081-3

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A scoping review of ‘Pacing’ for management of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): lessons learned for the long COVID pandemic

• Nilihan E. M. Sanal-Hayes 1 , 7 ,
• Marie Mclaughlin 1 , 8 ,
• Lawrence D. Hayes 1 ,
• Jacqueline L. Mair   ORCID: orcid.org/0000-0002-1466-8680 2 , 3 ,
• Jane Ormerod 4 ,
• David Carless 1 ,
• Natalie Hilliard 5 ,
• Rachel Meach 1 ,
• Joanne Ingram 6 &
• Nicholas F. Sculthorpe 1  

Journal of Translational Medicine volume  21 , Article number:  720 ( 2023 ) Cite this article

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Controversy over treatment for people with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a barrier to appropriate treatment. Energy management or pacing is a prominent coping strategy for people with ME/CFS. Whilst a definitive definition of pacing is not unanimous within the literature or healthcare providers, it typically comprises regulating activity to avoid post exertional malaise (PEM), the worsening of symptoms after an activity. Until now, characteristics of pacing, and the effects on patients’ symptoms had not been systematically reviewed. This is problematic as the most common approach to pacing, pacing prescription, and the pooled efficacy of pacing was unknown. Collating evidence may help advise those suffering with similar symptoms, including long COVID, as practitioners would be better informed on methodological approaches to adopt, pacing implementation, and expected outcomes.

In this scoping review of the literature, we aggregated type of, and outcomes of, pacing in people with ME/CFS.

Eligibility criteria

Original investigations concerning pacing were considered in participants with ME/CFS.

Sources of evidence

Six electronic databases (PubMed, Scholar, ScienceDirect, Scopus, Web of Science and the Cochrane Central Register of Controlled Trials [CENTRAL]) were searched; and websites MEPedia, Action for ME, and ME Action were also searched for grey literature, to fully capture patient surveys not published in academic journals.

A scoping review was conducted. Review selection and characterisation was performed by two independent reviewers using pretested forms.

Authors reviewed 177 titles and abstracts, resulting in 17 included studies: three randomised control trials (RCTs); one uncontrolled trial; one interventional case series; one retrospective observational study; two prospective observational studies; four cross-sectional observational studies; and five cross-sectional analytical studies. Studies included variable designs, durations, and outcome measures. In terms of pacing administration, studies used educational sessions and diaries for activity monitoring. Eleven studies reported benefits of pacing, four studies reported no effect, and two studies reported a detrimental effect in comparison to the control group.

Conclusions

Highly variable study designs and outcome measures, allied to poor to fair methodological quality resulted in heterogenous findings and highlights the requirement for more research examining pacing. Looking to the long COVID pandemic, our results suggest future studies should be RCTs utilising objectively quantified digitised pacing, over a longer duration of examination (i.e. longitudinal studies), using the core outcome set for patient reported outcome measures. Until these are completed, the literature base is insufficient to inform treatment practises for people with ME/CFS and long COVID.

Introduction

Post-viral illness occurs when individuals experience an extended period of feeling unwell after a viral infection [ 1 , 2 , 3 , 4 , 5 , 6 ]. While post-viral illness is generally a non-specific condition with a constellation of symptoms that may be experienced, fatigue is amongst the most commonly reported [ 7 , 8 , 9 ]. For example, our recent systematic review found there was up to 94% prevalence of fatigue in people following acute COVID-19 infection [ 3 ]. The increasing prevalence of long COVID has generated renewed interest in symptomology and time-course of post-viral fatigue, with PubMed reporting 72 articles related to “post-viral fatigue” between 2020 and 2022, but less than five for every year since 1990.

As the coronavirus pandemic developed, it became clear that a significant proportion of the population experienced symptoms which persisted beyond the initial viral infection, meeting the definition of a post-viral illness. Current estimates suggest one in eight people develop long COVID [ 10 ] and its symptomatology has repeatedly been suggested to overlap with clinical demonstrations of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). In a study by Wong and Weitzer [ 11 ], long COVID symptoms from 21 studies were compared to a list of ME/CFS symptoms. Of the 29 known ME/CFS symptoms the authors reported that 25 (86%) were reported in at least one long COVID study suggesting significant similarities. Sukocheva et al. [ 12 ] reported that long COVID included changes in immune, cardiovascular, metabolic, gastrointestinal, nervous and autonomic systems. When observed from a pathological stance, this list of symptoms is shared with, or is similar to, the symptoms patients with ME/CFS describe [ 13 ]. In fact, a recent article reported 43% of people with long COVID are diagnosed with ME/CFS [ 13 ], evidencing the analogous symptom loads.

A striking commonality between long COVID and similar conditions such as ME/CFS is the worsening of symptoms including fatigue, pain, cognitive difficulties, sore throat, and/or swollen lymph nodes following exertion. Termed post exertional malaise (PEM) [ 14 , 15 , 16 , 17 ], lasting from hours to several days, it is arguably one of the most debilitating side effects experienced by those with ME/CFS [ 16 , 17 , 18 ]. PEM is associated with considerably reduced quality of life amongst those with ME/CFS, with reduced ability to perform activities of daily living, leading to restraints on social and family life, mental health comorbidities such as depression and anxiety, and devastating employment and financial consequences [ 19 , 20 , 21 , 22 ]. At present, there is no cure or pharmacological treatments for PEM, and therefore, effective symptom management strategies are required. This may be in part because the triggers of PEM are poorly understood, and there is little evidence for what causes PEM, beyond anecdotal evidence. The most common approach to manage PEM is to incorporate activity pacing into the day-to-day lives of those with ME/CFS with the intention of reducing the frequency of severity of bouts of PEM [ 23 ]. Pacing is defined as an approach where patients are encouraged to be as active as possible within the limits imposed by the illness [ 23 , 24 , 25 ]. In practice, pacing requires individuals to determine a level at which they can function, but which does not lead to a marked increase in fatigue and other symptoms [ 26 , 27 ].

Although long COVID is a new condition [ 3 , 14 ], the available evidence suggests substantial overlap with the symptoms of conditions such as ME/CFS and it is therefore pragmatic to consider the utility of management strategies (such as pacing) used in ME/CFS for people with long COVID. In fact, a recent Delphi study recommended that management of long COVID should incorporate careful pacing to avoid PEM relapse [ 28 ]. This position was enforced by a multidisciplinary consensus statement considering treatment of fatigue in long COVID, recommending energy conservation strategies (including pacing) for people with long COVID [ 29 ]. Given the estimated > 2 million individuals who have experienced long COVID in the UK alone [ 30 , 31 , 32 ], there is an urgent need for evidence-based public health strategies. In this context, it seems pragmatic to borrow from the ME/CFS literature.

From a historical perspective, the 2007 NICE guidelines for people with ME/CFS advised both cognitive behavioural therapy (CBT) and graded exercise therapy (GET) should be offered to people with ME/CFS [ 33 ]. As of the 2021 update, NICE guidelines for people with ME/CFS do not advise CBT or GET, and the only recommended management strategy is pacing [ 34 ]. In the years between changes to these guidelines, the landmark PACE trial [ 35 ] was published in 2011. This large, randomised control trial (RCT; n = 639) compared pacing with CBT and reported GET and CBT were more effective than pacing for improving symptoms. Yet, this study has come under considerable criticism from patient groups and clinicians alike [ 36 , 37 , 38 , 39 ]. This may partly explain why NICE do not advise CBT or GET as of 2021, and only recommend pacing for symptom management people with ME/CFS [ 34 ]. There has been some controversy over best treatment for people with ME/CFS in the literature and support groups, potentially amplified by the ambiguity of evidence for pacing efficacy and how pacing should be implemented. As such, before pacing can be advised for people with long COVID, it is imperative previous literature concerning pacing is systematically reviewed. This is because a consensus is needed within the literature for implementing pacing so practitioners treating people with ME/CFS or long COVID can do so effectively. A lack of agreement in pacing implementation is a barrier to adoption for both practitioners and patients. Despite several systematic reviews concerning pharmacological interventions or cognitive behavioural therapy in people with ME/CFS [ 36 , 40 , 41 ], to date, there are no systematic reviews concerning pacing.

Despite the widespread use of pacing, the literature base is limited and includes clinical commentaries, case studies, case series, and few randomised control trials. Consequently, while a comprehensive review of the effects of pacing in ME/CFS is an essential tool to guide symptom management advice, the available literature means that effective pooling of data is not feasible [ 42 ] and therefore, a traditional systematic review and meta-analysis, with a tightly focussed research question would be premature [ 43 ]. Consequently, we elected to undertake a scoping review. This approach retains the systematic approach to literature searching but aims to map out the current state of the research [ 43 ]. Using the framework of Arksey and O'Malley [ 44 ], a scoping review aims to use a broad set of search terms and include a wide range of study designs and methods (in contrast to a systematic review [ 44 ]). This approach, has the benefit of clarifying key concepts, surveying current data collection approaches, and identifying critical knowledge gaps.

We aimed to provide an overview of existing literature concerning pacing in ME/CFS. Our three specific objectives of this scoping review were to (1) conduct a systematic search of the published literature concerning ME/CFS and pacing, (2) map characteristics and methodologies used, and (3) provide recommendations for the advancement of the research area.

Protocol and registration

The review was conducted and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for scoping reviews (PRISMA-ScR) guidelines [ 45 ] and the five-stage framework outlined in Arksey and O’Malley [ 44 ]. Registration is not recommended for scoping reviews.

Studies that met the following criteria were included in this review: (1) published as a full-text manuscript; (2) not a review; (3) participants with ME/CFS; (4) studies employed a pacing intervention or retrospective analysis of pacing or a case study of pacing. Studies utilising sub-analysis of the pacing, graded activity, and cognitive behaviour therapy: a randomised evaluation (PACE) trial were included as these have different outcome measures and, as this is not a meta-analysis, this will not influence effect size estimates. Additionally, due to the paucity of evidence, grey literature has also been included in this review.

Search strategy

The search strategy consisted of a combination of free-text and MeSH terms relating to ME/CFS and pacing, which were developed through an examination of published original literature and review articles. Example search terms for PubMed included: ‘ME/CFS’ OR ‘ME’ OR ‘CFS’ OR ‘chronic fatigue syndrome’ OR ‘PEM’ OR ‘post exertional malaise’ OR ‘pene’ OR ‘post-exertion neurogenic exhaust’ AND ‘pacing’ OR ‘adaptive pacing’. The search was performed within title/abstract. Full search terms can be found in Additional file 1 .

Information sources

Six electronic databases [PubMed, Scholar, ScienceDirect, Scopus, Web of Science, and the Cochrane Central Register of Controlled Trials (CENTRAL)] were searched to identify original research articles published from the earliest available date up until 02/02/2022. Additional records were identified through reference lists of included studies. ‘Grey literature’ repositories including MEPedia, Action for ME, and ME Action were also searched with the same terms.

Study selection and data items

Once each database search was completed and manuscripts were sourced, all studies were downloaded into a single reference list (Zotero, version 6.0.23) and duplicates were removed. Titles and abstracts were screened for eligibility by two reviewers independently and discrepancies were resolved through discussion between reviewers. Subsequently, full text papers of potentially relevant studies were retrieved and assessed for eligibility by the same two reviewers independently. Any uncertainty by reviewers was discussed in consensus meetings and resolved by agreement. Data extracted from each study included sample size, participant characteristics, study design, trial registration details, study location, pacing description (type), intervention duration, intervention adherence, outcome variables, and main outcome data. Descriptions were extracted with as much detail as was provided by the authors. Study quality was assessed using the Physiotherapy Evidence Database (PEDro) scale [ 46 , 47 ].

Role of the funding source

The study sponsors had no role in study design, data collection, analysis, or interpretation, nor writing the report, nor submitting the paper for publication.

Study selection

After the initial database search, 281 records were identified (see Fig.  1 ). Once duplicates were removed, 177 titles and abstracts were screened for inclusion resulting in 22 studies being retrieved as full text and assessed for eligibility. Of those, five were excluded, and 17 articles remained and were used in the final qualitative synthesis.

Schematic flow diagram describing exclusions of potential studies and final number of studies. RCT = randomized control trial. CT = controlled trial. UCT = uncontrolled trial

Study characteristics

Study characteristics are summarised in Table 1 . Of the 17 studies included, three were randomised control trials (RCTs [ 35 , 48 , 49 ]); one was an uncontrolled trial [ 50 ]; one was a case series [ 51 ]; one was a retrospective observational study [ 52 ], two were prospective observational studies [ 53 , 54 ]; four were cross-sectional observational studies [ 25 , 55 , 56 ]; and five were cross-sectional analytical studies [ 57 , 58 , 59 , 60 , 61 ] including sub-analysis of the PACE trial [ 35 , 56 , 59 , 61 ]. Seven of the studies were registered trials [ 35 , 48 , 49 , 50 , 56 , 57 , 58 ]. Diagnostic criteria for ME/CFS are summarised in Table 2 .

Types of pacing

Pacing interventions.

Of the 17 studies included, five implemented their own pacing interventions and will be discussed in this section. Sample sizes ranged from n = 7 in an interventional case series [ 51 ] to n = 641 participants in the largest RCT [ 35 ]. The first of these five studies considered an education session on pacing and self-management as the ‘pacing’ group, and a ‘pain physiology education’ group as the control group [ 49 ]. Two studies included educational sessions provided by a therapist plus activity monitoring via ActiGraph accelerometers [ 51 ] and diaries [ 48 ] at baseline and follow-up. In the first of these two studies, Nijs and colleagues [ 51 ] implemented a ‘self-management program’ which asked patients to estimate their current physical capabilities prior to commencing an activity and then complete 25–50% less than their perceived energy envelope. They[ 51 ] did not include a control group and had a sample size of only n = 7. Six years later, the same research group [ 48 ] conducted another pacing study which utilised relaxation as a comparator group (n = 12 and n = 14 in the pacing and relaxation groups, respectively). The pacing group underwent a pacing phase whereby participants again aimed to complete 25–50% less than their perceived energy envelope, followed by a gradual increase in exercise after the pacing phase (the total intervention spanned three weeks, and it is unclear how much was allocated to pacing, and how much to activity increase). Therefore, it could be argued that Kos et al. [ 48 ] really assessed pacing followed by a gradual exercise increase as outcome measures were assessed following the graded activity phase. Another pacing intervention delivered weekly educational sessions for six weeks and utilised a standardised rehabilitation programme using the ‘activity pacing framework’ [ 50 ] in a single-arm, no comparator group feasibility study. Finally, the PACE trial adopted an adaptive pacing therapy intervention consisting of occupational therapists helping patients to plan and pace activities utilising activity diaries to identify activities associated with fatigue and staying within their energy envelope [ 35 ]. This study incorporated standard medical care, cognitive behavioural therapy (CBT) and graded exercise therapy (GET) as comparator groups [ 35 ]. It is worth noting that the pacing group and the CBT group were both ‘encouraged’ to increase physical activity levels as long as participants did not exceed their energy envelope. Although not all five intervention studies explicitly mentioned the “Energy Envelope Theory”, which dictates that people with ME/CFS should not necessarily increase or decrease their activity levels, but moderate activity and practice energy conservation [ 62 ], all intervention studies used language analogous to this theory, such as participants staying within limits, within capacity, or similar.

The interventions included in this review were of varying durations, from a single 30-min education session [ 49 ], a 3-week (one session a week) educational programme [ 51 ], a 3-week (3 × 60–90 min sessions/week) educational programme [ 48 ], a 6-week rehabilitation programme [ 50 ], to a 24-week programme [ 35 ]. Intervention follow-up durations also varied across studies from immediately after [ 49 ], 1-week [ 51 ], 3-weeks [ 48 ], 3-months [ 50 ], and 1-year post-intervention [ 35 ].

Observational studies of pacing

Eight studies were observational and, therefore, included no intervention. Observational study sample sizes ranged from 16 in a cross-sectional interview study [ 25 ] to 1428 in a cross-sectional survey [ 52 ]. One study involved a retrospective analysis of participants’ own pacing strategies varying from self-guided pacing or pacing administered by a therapist compared with implementation of CBT and GET [ 52 ]. Five involved a cross-sectional analysis of participants own pacing strategies which varied from activity adjustment, planning and acceptance [ 50 , 55 ], and the Energy Envelope method [ 58 , 60 ]. Two studies were prospective observational studies investigating the Energy Envelope theory [ 53 , 54 ]. Four studies [ 56 , 57 , 59 , 61 ] included in this review involved sub-analysis of results of the PACE trial [ 35 ].

Outcome measures

Quantitative health outcomes.

ME/CFS severity and general health status were the most common outcome measures across studies (16/17) [ 35 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 63 ]. Studies utilised different instruments, including the Short-Form 36 (SF-36; 8/16) [ 35 , 51 , 53 , 54 , 56 , 57 , 58 , 60 ], SF-12 (2/16) [ 50 , 63 ], ME symptom and illness severity (2/16) [ 52 , 55 ], Patient health (PHQ-15; 1/16) [ 59 ], DePaul symptom questionnaire (DSQ; 1/16) [ 58 ], and the Patient health questionnaire-9 (1/16) [ 50 ]. Additionally, some studies used diagnostic criteria for ME/CFS as an outcome measure to determine recovery [ 57 , 59 , 61 ].

Pain was assessed by most included studies (11/17) [ 35 , 49 , 50 , 51 , 53 , 54 , 55 , 57 , 59 , 60 , 61 , 63 ]. Two studies [ 59 , 61 ] included the international CDC criteria for CFS which contain five painful symptoms central to a diagnosis of CFS: muscle pain and joint pain. Other methods of assessment included Brief Pain Inventory (1/11) [ 53 ], Chronic Pain Coping Inventory (CPCI; 1/11) [ 49 ], Pain Self Efficacy Questionnaire (PSEQ; 1/11) [ 50 ], Tampa Scale for Kinesiophobia–version CFS (1/11) [ 49 ], algometry (1/11) [ 49 ], Knowledge of Neurophysiology of Pain Test (1/12) [ 49 ], Pain Catastrophizing Scale (1/11) [ 49 ], Pain Anxiety Symptoms Scale short version (PASS-20; 1/11) [ 50 ], Pain Numerical Rating Scale (NRS; 1/11) [ 63 ].

Fatigue or post-exertional malaise was assessed by 11 of the 17 studies [ 35 , 48 , 50 , 51 , 53 , 54 , 56 , 57 , 60 , 61 , 63 ]. Again, measurement instruments were divergent between studies and included the Chalder Fatigue Questionnaire (CFQ; 4/11) [ 35 , 50 , 57 , 63 ], Fatigue Severity Scale (2/11) [ 53 , 60 ], the Chronic Fatigue Syndrome Medical Questionnaire (1/11) [ 60 ], and Checklist Individual Strength (CIS; 2/11) [ 48 , 51 ].

Anxiety and depression were also common outcome measures, utilised by four studies (4/17) [ 50 , 53 , 59 , 63 ]. These were also assessed using different instruments including Hospital Anxiety and Depression Scale (HADS; 2/4) [ 59 , 63 ], Generalised Anxiety Disorder Assessment (1/4 [ 50 ]), Beck Depression Inventory (BDI-II; 1/4) [ 53 ], Beck Anxiety Inventory (BAI; 1/4) [ 53 ], and Perceived Stress Scale (PSS; 1/4) [ 53 ].

Outcome measures also included sleep (2/17) [ 53 , 59 ], assessed by The Pittsburgh Sleep Quality Index (1/2) [ 53 ] and Jenkins sleep scale (1/2) [ 59 ]; and quality of life (2/17) [ 50 , 53 ] as assessed by the EuroQol five-dimensions, five-levels (EQ-5D-5L; 1/2) [ 50 ] and The Quality-of-Life Scale (1/2) [ 53 ]. Self-Efficacy was measured in four studies [ 50 , 53 , 59 , 60 ], assessed by the Brief Coping Orientation to Problems Experienced Scale (bCOPE; 1/4) [ 60 ] and the Chronic Disease Self-Efficacy measure (3/4) [ 50 , 53 , 59 ].

Quantitative evaluation of pacing

Some studies (4/17) [ 25 , 50 , 52 , 63 ] included assessments of the participants’ experiences of pacing, using the Activity Pacing Questionnaire (APQ-28; 1/4 [ 50 ], APQ-38 (2/4) [ 25 , 63 ]), a re-analysis of the 228 question survey regarding treatment (1/4) [ 52 ] originally produced by the ME Association [ 55 ], and qualitative semi-structured telephone interviews regarding appropriateness of courses in relation to individual patient needs (1/4) [ 25 ]. The APQ-28 and -38 have been previously validated, but the 228-question survey has not. When outcome measures included physical activity levels (4/17), the Canadian Occupational Performance Measure (COPM) was used in two studies [ 48 , 51 ], and two studies used accelerometers to record physical activity [ 51 , 54 ]. Of these two studies, Nijs [ 51 ] examined accelerometery after a 3-week intervention based on the Energy Envelope Theory and Brown et al. [ 54 ] evaluated the Energy Envelope Theory of pacing over 12 months.

Other outcomes

Two [ 53 , 59 ] of the 17 studies included structured clinical interviews for the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) to assess psychiatric comorbidity and psychiatric exclusions. One study included a disability benefits questionnaire [ 55 ], and one study included employment and education questionnaire [ 55 ]. Additionally, satisfaction of primary care was also used as an outcome measure (2/17) [ 25 , 55 ] assessed using the Chronic Pain Coping Inventory (CPCI).

Efficacy of pacing interventions

The majority of studies (12/17) [ 25 , 48 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 58 , 60 , 63 ] highlighted improvements in at least one outcome following pacing (Fig.  2 ). When the effect of pacing was assessed by ME symptomology and general health outcomes, studies reported pacing to be beneficial [ 25 , 50 , 51 , 53 , 54 , 55 , 56 , 58 ]. It is worth noting however that pacing reportedly worsened ME symptoms in 14% of survey respondents, whilst improving symptoms in 44% of respondents [ 52 ]. Most studies using fatigue as an outcome measure reported pacing to be efficacious (7/10) [ 50 , 51 , 53 , 54 , 56 , 60 , 63 ]. However, one study reported no change in fatigue with a pacing intervention (1/10) [ 35 ], and 2/10 studies [ 53 , 63 ] reported a worsening of fatigue with pacing. Physical function was used to determine the efficacy of pacing in 11 studies [ 35 , 48 , 50 , 51 , 53 , 54 , 56 , 58 , 59 , 60 , 63 ]. Of these, the majority found pacing improved physical functioning (8/10) [ 48 , 50 , 51 , 53 , 54 , 56 , 58 , 60 ], with 1/10 [ 35 ] studies reporting no change in physical functioning, and 1/10 [ 59 ] reporting a worsening of physical functioning from pre- to post-pacing. Of the seven studies [ 35 , 49 , 50 , 51 , 53 , 54 , 60 ] which used pain to assess pacing efficacy, 4/7 [ 50 , 51 , 53 , 60 ] reported improvements in pain and 3/7 [ 35 , 51 , 53 ] reported no change in pain scores with pacing. All studies reporting quality of life (1/1) [ 53 ], self-efficacy (3/3) [ 50 , 53 , 59 ], sleep (2/2) [ 53 , 59 ], and depression and anxiety (4/4) [ 50 , 53 , 59 , 63 ], found pacing to be efficacious for ME/CFS participants.

Bubble plot displaying number of studies reporting each domain (x-axis) and the percentage of studies reporting improvement with pacing (y-axis), including a coloured scale of improvement from 0–100%. PEM = post-exertional malaise, 6MWT = 6-min walk time, CFS = chronic fatigue syndrome, DSQ = DePaul Symptom Questionnaire, PA = Physical Activity, HRQOL = Health-related quality of life, COPM = The Canadian Occupational Performance Measure

Participant characteristics

The majority of studies (10/17) [ 25 , 50 , 52 , 53 , 54 , 58 , 59 , 60 , 61 , 63 ] did not report age of the participants. For those which did report age, this ranged from 32 ± 14 to 43 ± 13 years. Where studies reported sex (11/17) [ 35 , 48 , 49 , 50 , 51 , 54 , 55 , 56 , 57 , 58 , 60 ], this was predominantly female, ranging from 75 to 100% female. Only six studies [ 35 , 54 , 56 , 57 , 58 , 60 ] reported ethnicity, with cohorts predominantly Caucasian (94–98%). Time since diagnosis was mostly unreported (12/17) [ 25 , 48 , 49 , 50 , 52 , 53 , 54 , 58 , 59 , 60 , 61 , 63 ] but ranged from 32 to 96 months, with a cross-sectional survey reporting 2% of the participants were diagnosed 1–2 years previously; 6% 3–4 years since diagnosis; 13% 3–4 years since diagnosis; 12% 5–6 years since diagnosis; 20% 7–10 years since diagnosis; 29% 11–21 years since diagnosis; 13% 21–30 years since diagnosis; and 5% > 30 years since diagnosis. Of the studies which reported comorbidities of the participants (6/17) [ 25 , 35 , 50 , 56 , 57 , 63 ], the comorbidities were chronic pain, depressive disorder, psychiatric disorder.

Study location

Of the 17 studies, 14 were from Europe [ 25 , 35 , 48 , 49 , 50 , 51 , 52 , 55 , 56 , 57 , 58 , 59 , 61 , 63 ], and three from North America [ 53 , 54 , 60 ]. Of the 14 studies[ 25 , 35 , 48 , 49 , 50 , 51 , 52 , 55 , 56 , 57 , 58 , 59 , 61 , 63 ] from Europe, ten [ 25 , 35 , 50 , 52 , 55 , 56 , 57 , 58 , 59 , 61 , 63 ] were conducted in the United Kingdom, three in Belgium [ 48 , 49 , 51 ], and one was a multicentred study between the United Kingdom and Norway [ 58 ].

Recruitment strategy

Of the 17 studies, three [ 53 , 54 , 60 ] used announcements in a newspaper and physician referrals to recruit participants, two [ 50 , 63 ] recruited patients referred by a consultant from a National Health Service (NHS) Trust following a pain diagnosis, two [ 52 , 55 ] concerned online platforms on the web, two [ 59 , 61 ] recruited from secondary care clinics, and two used the PACE trial databases [ 56 , 57 ]. Moreover, one study recruited from the hospital [ 58 ], one from physiotherapist referrals [ 25 ], two from specialist clinic centres [ 35 , 64 ], one from waiting list of rehabilitation centre [ 48 ], and one from medical files [ 49 ].

Study settings

Ten studies were carried out in hospital and clinic setting [ 25 , 35 , 48 , 49 , 50 , 51 , 58 , 59 , 61 , 63 ]. Two studies were performed on online platforms [ 52 , 55 ]. Three studies did not report study setting [ 53 , 54 , 60 ]. Two studies generated output from PACE trial databases [ 56 , 57 ]

Adherence and feasibility

All five intervention studies reported adherence rates (which they defined as number of sessions attended), which ranged from 4–44% (4% [ 49 ], 8% [ 35 ], 25% [ 48 ], 29% [ 51 ], and 44% [ 50 ]). One study reported the median number of rehabilitation programme sessions attended was five out of six possible sessions, with 58.9% [ 50 ] participants attending ≥ 5 sessions; 83.2% participants attending at least one educational session on activity pacing and 56.1% attending both activity pacing sessions.

This scoping review summarises the existing literature, with a view to aid physicians and healthcare practitioners better summarise evidence for pacing in ME/CFS and use this knowledge for other post-viral fatiguing conditions. Overall, studies generally reported pacing to be beneficial for people with ME/CFS. The exception to this trend is the controversial PACE trial [ 36 , 37 , 38 , 39 ], which we will expand on in subsequent sections. We believe information generated within this review can facilitate discussion of research opportunities and issues that need to be addressed in future studies concerning pacing, particularly given the immediate public health issue of the long COVID pandemic. As mentioned, we found some preliminary evidence for improved symptoms following pacing interventions or strategies. However, we wish to caution the reader that the current evidence base is extremely limited and hampered by several limitations which preclude clear conclusions on the efficacy of pacing. Firstly, studies were of poor to fair methodological quality (indicated by the PEDro scores), often with small sample sizes, and therefore unknown power to detect change. Moreover, very few studies implemented pacing, with most studies merely consulting on people’s views on pacing. This may of course lead to multiple biases such as reporting, recruitment, survivorship, confirmation, availability heuristic, to name but a few. Thus, there is a pressing need for more high-quality intervention studies. Secondly, the reporting of pacing strategies used was inconsistent and lacked detail, making it difficult to describe current approaches, or implement them in future research or symptom management strategies. Furthermore, outcome evaluations varied greatly between studies. This prevents any appropriate synthesis of research findings.

The lack of evidence concerning pacing is concerning given pacing is the only NICE recommended management strategy for ME/CFS following the 2021 update [ 34 ]. Given the analogous nature of long COVID with ME/CFS, patients and practitioners will be looking to the ME/CFS literature for guidance for symptom management. There is an urgent need for high quality studies (such as RCTs) investigating the effectiveness of pacing and better reporting of pacing intervention strategies so that clear recommendations can be made to patients. If this does not happen soon, there will be serious healthcare and economic implications for years to come [ 65 , 66 ].

Efficacy of pacing

Most studies (12/17) highlighted improvements in at least one outcome measure following pacing. Pacing was self-reported to be the most efficacious, safe, acceptable, and preferred form of activity management for people with ME/CFS [ 55 ]. Pacing was reported to improve symptoms and improve general health outcomes [ 25 , 50 , 52 , 58 , 63 ], fatigue and PEM [ 48 , 50 , 51 , 53 , 54 , 55 , 56 , 60 , 63 ], physical functioning [ 48 , 50 , 51 , 53 , 56 , 58 , 60 , 63 ], pain [ 25 , 50 , 55 , 63 ], quality of life [ 50 ], self-efficacy [ 50 , 53 ], sleep [ 53 , 55 ], and depression and anxiety [ 50 , 53 , 63 ]. These positive findings provide hope for those with ME/CFS, and other chronic fatiguing conditions such as long COVID, to improve quality of life through symptom management.

Conversely, some studies reported no effects of pacing on ME/CFS symptoms [ 52 ], fatigue, physical functioning [ 35 ], or pain scores [ 49 , 61 ]. Some studies even found pacing to have detrimental effects in those with ME/CFS, including a worsening of symptoms in 14% of survey participants recalling previous pacing experiences [ 52 ]. Furthermore, a worsening of fatigue [ 35 , 59 ], and physical functioning from pre- to post-pacing [ 35 , 57 , 59 , 61 ] was reported by the PACE trial and sub-analysis of the PACE trial [ 56 , 57 , 61 ]. The PACE trial [ 35 ], a large RCT (n = 639) comparing pacing with CBT and GET, reported GET and CBT were more effective for reducing ME/CFS-related fatigue and improving physical functioning than pacing. However, the methodology and conclusions from the PACE trial have been heavily criticised, mainly due to the authors lowering the thresholds they used to determine improvement [ 36 , 37 , 38 , 67 ]. With this in mind, Sharpe et al. [ 56 ] surveyed 75% of the participants from the PACE trial 1-year post-intervention and reported pacing improved fatigue and physical functioning, with effects similar to CBT and GET.

Lessons for pacing implementation

All pacing intervention studies (5/5) implemented educational or coaching sessions. These educational components were poorly reported in terms of the specific content and how and where they had been developed, with unclear pedagogical approaches. Consequently, even where interventions reported reduction in PEM or improved symptoms, it would be impossible to transfer that research into practice, future studies, or clinical guidance, given the ambiguity of reporting. Sessions typically contained themes of pacing such as activity adjustment (decrease, break-up, and reschedule activities based on energy levels), activity consistency (maintaining a consistently low level of activity to prevent PEM), activity planning (planning activities and rest around available energy levels), and activity progression (slowly progressing activity once maintaining a steady baseline) [ 35 , 48 , 49 , 50 , 51 ]. We feel it is pertinent to note here that although activity progression has been incorporated as a pacing strategy in these included studies, some view activity progression as a form of GET. The NICE definition of GET is “first establishing an individual's baseline of achievable exercise or physical activity, then making fixed incremental increases in the time spent being physically active” [ 34 ]. Thus, this form of pacing can also be considered a type of ‘long-term GET’ in which physical activity progression is performed over weeks or months with fixed incremental increases in time spent being physically.

Intervention studies attempted to create behaviour change, through educational programmes to modify physical activity, and plan behaviours. However, none of these studies detailed integrating any evidence-based theories of behaviour change [ 68 ] or reported using any frameworks to support behaviour change objectives. This is unfortunate since there is good evidence that theory-driven behaviour change interventions result in greater intervention effects [ 69 ]. Indeed, there is a large body of work regarding methods of behaviour change covering public health messaging, education, and intervention design, which has largely been ignored by the pacing literature. Interventions relied on subjective pacing (5/5 studies), with strategies including keeping an activity diary (3/5 studies) to identify links between activity and fatigue [ 35 , 48 , 50 ]. Given the high prevalence of ‘brain fog’ within ME/CFS [ 70 , 71 , 72 , 73 ], recall may be extremely difficult and there is significant potential for under-reporting. Other strategies included simply asking participants to estimate energy levels available for daily activities (2/5 studies [ 48 , 51 ]). Again, this is subjective and relies on participants’ ability to recall previous consequences of the activity. Other methods of activity tracking and measuring energy availability, such as wearable technology [ 74 , 75 , 76 , 77 , 78 ] could provide a more objective measure of adherence and pacing strategy fidelity in future studies. Despite technology such as accelerometers being widely accessible since well-before the earliest interventional study included in this review (which was published in 2009), none of the interventional studies utilised objective activity tracking to track pacing and provide feedback to participants. One study considered accelerometery alongside an activity diary [ 51 ]. However, accelerometery was considered the outcome variable, to assess change in activity levels from pre- to post-intervention and was not part of the intervention itself (which was one pacing coaching sessions per week for 3 weeks). Moreover, most research-grade accelerometers cannot be used as part of the intervention since they have no ability to provide continuous feedback and must be retrieved by the research team in order to access any data. Consequently, their use is mostly limited to outcome assessments only. As pacing comprises a limit to physical activity to prevent push-crash cycles, it is an astonishing observation from this scoping review that only two studies objectively measured physical activity to quantify changes to activity as a result of pacing [ 51 , 54 ]. If the aim of pacing is to reduce physical activity, or reduce variations in physical activity (i.e., push-crash cycles), only two studies have objectively quantified the effect pacing had on physical activity, so it is unclear whether pacing was successfully implemented in any of the other studies.

By exploring the pacing strategies previously used, in both intervention studies and more exploratory studies, we can identify and recommend approaches to improve symptoms of ME/CFS. These approaches can be categorised as follows: activity planning, activity consistency, activity progression, activity adjustment and staying within the Energy Envelope [ 50 , 53 , 60 , 63 ]. Activity planning was identified as a particularly effective therapeutic strategy, resulting in improvement of mean scores of all symptoms included in the APQ-28, reducing current pain, improvement of physical fatigue, mental fatigue, self-efficacy, quality of life, and mental and physical functioning [ 50 ]. Activity planning aligns with the self-regulatory behaviour change technique ‘Action Planning’ [ 79 ] which is commonly used to increase physical activity behaviour. In the case of ME/CFS, activity planning is successfully used to minimise rather than increase physical activity bouts to prevent expending too much energy and avoid PEM. Activity consistency, meaning undertaking similar amounts of activity each day, was also associated with reduced levels of depression, exercise avoidance, and higher levels of physical function [ 63 ]. Activity progression was associated with higher levels of current pain. Activity adjustment associated with depression and avoidance, and lower levels of physical function [ 63 ]. Staying within the Energy Envelope was reported to reduce PEM severity [ 53 , 60 ], improve physical functioning [ 53 , 60 ] and ME/CFS symptom scores [ 53 ], and more hours engaged in activity than individuals with lower available energy [ 53 ]. These results suggest that effective pacing strategies would include activity planning, consistency, and energy management techniques while avoiding progression. This data is, of course, limited by the small number of mostly low-quality studies and should be interpreted with some caution. Nevertheless, these are considerations that repeatedly appear in the literature and, as such, warrant deeper investigation. In addition, and as outlined earlier, most studies are relatively old, and we urgently need better insight into how modern technologies, particularly longitudinal activity tracking and contemporaneous heart-rate feedback, might improve (or otherwise) adaptive pacing. Such longitudinal tracking would also enable activities and other behaviours (sleep, diet, stress) to be linked to bouts of PEM. Linking would enable a deeper insight into potential PEM triggers and mitigations that might be possible.

The PACE trial

We feel it would be remiss of us to not specifically address the PACE trial within this manuscript, as five of the 17 included studies resulted from the PACE trial [ 35 , 56 , 57 , 59 , 61 ]. There has been considerable discussion around the PACE trial, which has been particularly divisive and controversial [ 37 , 38 , 39 , 59 , 67 , 80 , 81 ]. In the PACE trial, GET and CBT were deemed superior to pacing by the authors. Despite its size and funding, the PACE trial has received several published criticisms and rebuttals. Notably, NICE's most recent ME/CFS guideline update removed GET and CBT as suggested treatment options, which hitherto had been underpinned by the PACE findings. While we will not restate the criticisms and rebuttals here, what is not in doubt, is that the PACE trial has dominated discussions of pacing, representing almost a third of all the studies in this review. However, the trial results were published over a decade ago, with the study protocol devised almost two decades ago [ 82 ]. The intervening time has seen a revolution in the development of mobile and wearable technology and an ability to remotely track activity and provide real-time feedback in a way which was not available at that time. Furthermore, there has been no substantive research since the PACE trial that has attempted such work. Indeed, possibly driven by the reported lack of effect of pacing in the PACE trial, this review has demonstrated the dearth of progress and innovation in pacing research since its publication. Therefore, regardless of its findings or criticisms, the pacing implementation in the PACE trial is dated, and there is an urgent need for more technologically informed approaches to pacing research.

Limitations of the current evidence

The first limitation to the literature included in this scoping review is that not all studies followed the minimum data set (MDS) of patient-reported outcome measures (PROMs) agreed upon by the British Association of CFS/ME Professionals (BACME) (fatigue, sleep quality, self-efficacy, pain/discomfort, anxiety/depression, mobility, activities of daily living, self-care, and illness severity) [ 83 , 84 ]. All but one study included in this review measured illness severity, most studies included fatigue and pain/discomfort, and some studies included assessments of anxiety/depression. There was a lack of quantitative assessment of sleep quality, self-efficacy, mobility, activities of daily living, and self-care. Therefore, studies did not consistently capture the diverse nature of the symptoms experienced, with crucial domains missing from the analyses. The MDS of PROMs were established in 2012 [ 83 , 84 ] and therefore, for studies published out prior to 2012, these are not applicable [ 35 , 49 , 51 , 53 , 54 ]. However, for the 12 studies carried out after this time, the MDS should have been considered elucidate the effects of pacing on ME/CFS. Importantly, despite PEM being a central characteristic of ME/CFS, only two studies included PEM as an outcome measure [ 55 , 60 ]. This may be because of the difficulty of accurately measuring fluctuating symptoms, as PEM occurs multiple times over a period of months, and therefore pre- to post- studies and cross-sectional designs cannot adequately capture PEM incidence. Therefore, it is likely studies opted for measuring general fatigue instead. More appropriate longitudinal study designs are required to track PEM over time to capture a more representative picture of PEM patterns. Secondly, reporting of participant characteristics was inadequate, but in the studies that did describe participants, characteristics were congruent with the epidemiological literature and reporting of ME/CFS populations (i.e., 60–65% female) [ 85 ]. Therefore, in this respect, studies included herein were representative samples. However, the lack of reporting of participant characteristics limits inferences we can draw concerning any population-related effects (i.e. whether older, or male, or European, or people referred by a national health service would be more or less likely to respond positively to pacing). Thirdly, comparison groups (where included) were not ideal, with CBT or GET sometimes used as comparators to pacing [ 35 ], and often no true control group included. Penultimately, there is a distinct lack of high-quality RCTs (as mentioned throughout this manuscript). Finally, in reference to the previous section, inferences from the literature are dated and do not reflect the technological capabilities of 2023.

Recommendations for advancement of the investigative area

It is clear from the studies included in this scoping review for the last decade or more, progress and innovation in pacing research have been limited. This is unfortunate for several reasons. People with ME/CFS or long COVID are, of course, invested in their recovery. From our patient and public involvement (PPI) group engagement, it is clear many are ahead of the research and are using wearable technology to track steps, heart rate, and, in some cases, heart rate variability to improve their own pacing practice. While the lack of progress in the research means this is an understandable response by patients, it is also problematic. Without underpinning research, patients may make decisions based on an individual report of trial-and-error approaches given the lack of evidence-based guidance.

A more technologically-informed pacing approach could be implemented by integrating wearable trackers [ 77 , 78 , 86 , 87 ] to provide participants with live updates on their activity and could be integrated with research-informed messaging aimed at supporting behaviour change, as has been trialled in other research areas [ 88 , 89 , 90 , 91 ]. However, more work is needed to evaluate how to incorporate wearable activity trackers and which metrics are most helpful.

A more technologically-informed approach could also be beneficial for longitudinal symptom tracking, particularly useful given the highly variable symptom loads of ME/CFS and episodic nature of PEM. This would overcome reliance on assessments at a single point in time (as the studies within this review conducted). Similarly, mobile health (mHealth) approaches also allow questionnaires to be digitised to make it easier for participants to complete if they find holding a pen or reading small font problematic [ 92 ]. Reminders and notifications can also be helpful for patients completing tasks [ 77 , 93 , 94 , 95 ]. This approach has the added advantage of allowing contemporaneous data collection rather than relying on pre- to post-intervention designs limited by recall bias. Future work must try to leverage these approaches, as unless we collect large data sets on symptoms and behaviours (i.e. activity, diet, sleep, and pharmacology) in people with conditions like ME/CFS we will not be able to leverage emerging technologies such as AI and machine learning to improve the support and care for people with these debilitating conditions. The key areas for research outline in the NICE guidelines (2021 update) speaks to this, with specific mention of improved self-monitoring strategies, sleep strategies, and dietary strategies, all of which can be measured using mHealth approaches, in a scalable and labour-inexpensive way.

The potential for existing pacing research to address the long COVID pandemic

There is now an urgent public health need to address long COVID, with over 200 million sufferers worldwide [ 30 ]. Given the analogous symptomology between ME/CFS and long COVID, and the lack of promising treatment and management strategies in ME/CFS, pacing remains the only strategy for managing long COVID symptoms. This is concerning as the quality of evidence to support pacing is lacking. Given long COVID has reached pandemic proportions, scalable solutions will be required. In this context, we propose that technology should be harnessed to a) deliver, but also b) evaluate, pacing. We recently reported on a just-in-time adaptive intervention to increase physical activity during the pandemic [ 78 ]. However, this method could be adapted to decrease or maintain physical activity levels (i.e., pacing) in long COVID. This method has the advantage of scalability and remote data collection, reducing resource commitments and participant burden, essential for addressing a condition with so many sufferers.

This review highlights the need for more studies concerning pacing in chronic fatiguing conditions. Future studies would benefit from examining pacing’s effect on symptomology and PEM with objectively quantified pacing, over a longer duration of examination, using the MDS. It is essential this is conducted as an RCT, given that in the case of long COVID, participants may improve their health over time, and it is necessary to determine whether pacing exerts an additional effect over time elapsing. Future studies would benefit from digitising pacing to support individuals with varying symptom severity and personalise support. This would improve accessibility and reduce selection bias, in addition to improving scalability of interventions. Finally, clinicians and practitioners should be cognisant of the strength of evidence reported in this review and should exert caution when promoting pacing in their patients, given the varying methods utilised herein.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Abbreviations

Activity Pacing Questionnaire

Beck Anxiety Inventory

Beck Depression Inventory

Brief Coping Orientation to Problems Experienced Scale

Canadian Occupational Performance Measure

Centers for disease control and prevention

Chalder Fatigue Questionnaire

Checklist Individual Strength

Chronic Pain Coping Inventory

Cognitive behavioural therapy

Cochrane Central Register of Controlled Trials

DePaul symptom questionnaire

EuroQol five-dimensions, five-levels questionnaire

Graded exercise therapy

Hospital Anxiety and Depression Scale

Myalgic encephalomyelitis/chronic fatigue syndrome

Pain Self Efficacy Questionnaire

Pain Anxiety Symptoms Scale short version

Pain Numerical Rating Scale

Patient health questionnaire

Patient reported outcome measures

Physiotherapy Evidence Database

Perceived Stress Scale

Post exertional malaise

Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for scoping reviews

Randomised control trial

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Authors’ contributions are given according to the CRediT taxonomy as follows: Conceptualization, N.E.M.S–H., M.M., L.D.H, and N.F.S.; methodology, N.E.M.S–H., M.M., L.D.H., and N.F.S.; software, N.E.M.S–H., M.M., L.D.H., and N.F.S.B.; validation, N.E.M.S–H., M.M., L.D.H, and N.F.S.; formal analysis, N.E.M.S–H., M.M., L.D.H., and N.F.S.; investigation, N.E.M.S–H., M.M., L.D.H., and N.F.S.; resources, L.D.H., J.O., D.C., N.H., J.L.M., and N.F.S.; data curation, N.E.M.S.-H., M.M., L.D.H., and N.F.S.; writing—original draft preparation, N.E.M.S.-H., M.M., L.D.H., and N.F.S.; writing—review and editing, N.E.M.S–H., M.M., L.D.H., J.O., D.C., N.H., R.M., J.L.M., J.I., and N.F.S.; visualisation, N.E.M.S–H. and M.M., supervision, N.F.S; project administration, N.E.M.S–H., M.M., L.D.H., and N.F.S.; funding acquisition, L.D.H., J.O., D.C., N.H., J.L.M., J.I., and N.F.S. All authors have read and agreed to the published version of the manuscript.

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Sanal-Hayes, N.E.M., Mclaughlin, M., Hayes, L.D. et al. A scoping review of ‘Pacing’ for management of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): lessons learned for the long COVID pandemic. J Transl Med 21 , 720 (2023). https://doi.org/10.1186/s12967-023-04587-5

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Diagnostic delay of sarcoidosis: an integrated systematic review

• Tergel Namsrai 1 ,
• Christine Phillips 4 ,
• Anne Parkinson 1 ,
• Dianne Gregory 1 , 2 ,
• Elaine Kelly 1 , 2 ,
• Matthew Cook 3 &
• Jane Desborough   ORCID: orcid.org/0000-0003-1406-4593 1  

Orphanet Journal of Rare Diseases volume  19 , Article number:  156 ( 2024 ) Cite this article

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Sarcoidosis is a chronic inflammatory granulomatous disease of unknown cause. Delays in diagnosis can result in disease progression and poorer outcomes for patients. Our aim was to review the current literature to determine the overall diagnostic delay of sarcoidosis, factors associated with diagnostic delay, and the experiences of people with sarcoidosis of diagnostic delay.

Three databases (PubMed/Medline, Scopus, and ProQuest) and grey literature sources were searched. Random effects inverse variance meta-analysis was used to pool mean diagnostic delay in all types of sarcoidosis subgroup analysis. Diagnostic delay was defined as the time from reported onset of symptoms to diagnosis of sarcoidosis.

We identified 374 titles, of which 29 studies were included in the review, with an overall sample of 1531 (694 females, 837 males). The overall mean diagnostic delay in all types of sarcoidosis was 7.93 months (95% CI 1.21 to 14.64 months). Meta-aggregation of factors related to diagnostic delay in the included studies identified three categories: (1) the complex and rare features of sarcoidosis, (2) healthcare factors and (3) patient-centred factors. Meta-aggregation of outcomes reported in case studies revealed that the three most frequent outcomes associated with diagnostic delay were: (1) incorrect diagnosis, (2) incorrect treatment and (3) development of complications/disease progression. There was no significant difference in diagnostic delay between countries with gatekeeper health systems (where consumers are referred from a primary care clinician to specialist care) and countries with non-gatekeeper systems. No qualitative studies examining people’s experiences of diagnostic delay were identified.

The mean diagnostic delay for sarcoidosis is almost 8 months, which has objective consequences for patient management. On the other hand, there is a paucity of evidence about the experience of diagnostic delay in sarcoidosis and factors related to this. Gaining an understanding of people’s experiences while seeking a diagnosis of sarcoidosis is vital to gain insight into factors that may contribute to delays, and subsequently inform strategies, tools and training activities aimed at increasing clinician and public awareness about this rare condition.

Trial registration

PROSPERO Registration number: CRD42022307236.

Introduction

Sarcoidosis is a multisystem granulomatous inflammatory disease of unknown cause, which can affect any organ, but primarily affects the lungs. Sarcoidosis can present as acute or chronic disease - acute sarcoidosis, with joint pain, erythema nodosum and hilar adenopathy, that resolves spontaneously; or chronic sarcoidosis with insidious onset and slow progression that continues to invade multiple systems. In studies using national patient registers the incidence appears to be highest in northern Europe at 11.5 per 100,000 per year in Sweden [ 1 ] and 11.3–14.8 per 100,000 per year in Denmark [ 2 ], There are significant intra-country differences attributable to ethnicity in the USA where African Americans have significantly higher rates of disease [ 1 , 2 ], earlier peak age of onset [ 3 ] and higher mortality [ 4 ]. The patterns of organ involvement [ 5 , 6 , 7 ] and gender distribution [ 3 , 4 , 8 ] vary between countries and within countries.

The reported delay of diagnosis in sarcoidosis ranges from 6 months [ 2 ] to 24 months [ 9 ]. Its complex clinical features, acute or chronic presentation, spontaneous or treatment-induced remission in some cases, and the absence of a single simple diagnostic test all contribute to challenges in timely diagnosis. In many cases, diagnosis hinges on tissue diagnosis and therefore a firm diagnosis might be delayed even when the diagnosis is suspected. Some of the most consequential extrapulmonary manifestations of sarcoidosis – neurological, ophthalmic, and cardiac – are among the most difficult to diagnose [ 8 , 9 , 10 , 11 ]. Spontaneous remission occurs frequently in sarcoidosis [ 12 ]; some studies report remission in half of the cases [ 13 ]. Diagnostic delay can occur with both acute and chronic presentations of sarcoidosis, but particularly for chronic presentations marked by slow progression and complex features, mimicking other diseases. Failure to initiate treatment for progressive pulmonary sarcoidosis [ 14 ] and many extrapulmonary manifestations of sarcoidosis can result in permanent organ damage [ 11 , 15 , 16 ]. Since the pathogenesis of sarcoidosis remains unknown, it is a diagnosis of exclusion. The differential diagnosis includes other causes of granulomas, which encompass infections, including mycobacteria, fungi and bacteria, occupational exposures such as beryllium and silica, sterile granulomatous inflammation, and lymphoma.

There is a paucity of research examining the diagnostic delay of sarcoidosis, including factors associated with diagnostic delay and people’s experiences from the time of symptom onset to diagnosis. Our aim was to systematically review the current evidence regarding the diagnostic delay of sarcoidosis and people’s experiences of this. This evidence may help to inform the development of strategies to enhance awareness of rare manifestations of sarcoidosis, enabling timely intervention when warranted for chronic and progressive sarcoidosis.

This systematic review was performed and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [ 17 ] and the Cochrane Handbook for Systematic Reviews [ 6 ]. It is registered with PROSPERO, an International prospective register of systematic reviews (registration number: CRD42022289830).

Literature search, study selection, and data extraction

A systematic electronic search of the literature was conducted using PubMed/Medline, Scopus, and ProQuest databases up to the 25th of May 2022, with no limitations. The search string was pre-developed and peer-reviewed using the PRESS checklist [ 18 ]. The final search string included “sarcoidosis” AND “delay in diagnosis” OR “diagnostic delay” OR “misdiagnosis” OR “time to diagnosis” OR “incorrect diagnosis” OR “missed diagnosis” OR “delayed diagnosis” without restrictions on study type, date, and language. A detailed search string and strategy are available in the published protocol [ 19 ]. Grey literature sources were searched up to the 25th of May 2022 in Open Access Theses and Dissertations ( https://oatd.org/ ), ProQuest thesis and dissertations, and the National Library of Australia. Manual reference searches were conducted on all review articles identified in the literature search.

There was no restriction on publication dates. All studies, both qualitative and quantitative, examining diagnostic delay, incorrect diagnosis, missed diagnosis or slow diagnosis of sarcoidosis in all age groups were included, except for review articles. Studies in languages other than English, German and Indonesian were excluded. Final search results were imported into a systematic review management software (Covidence) to facilitate reviewer collaboration [ 20 ].

Two authors conducted an independent screening of titles and abstracts followed by a full-text screening of articles using pre-developed PICOS eligibility criteria outlined in Table  1 . Articles that did not meet the eligibility criteria were excluded. Discrepancies were resolved in discussion with a third reviewer and through reaching a consensus. Included studies were quality appraised using the Mixed Methods Appraisal Tool (MMAT) [ 21 ]. A pre-developed and pre-piloted data extraction tool was used, and following further discussion after piloting, data describing the initial specialist and the presence/absence of gatekeeper health systems were also extracted.

Data analysis

General data preparation.

Diagnostic delay was defined in accordance with the included studies - from reported onset of symptoms to a diagnosis of sarcoidosis. In studies where mean diagnostic delay was presented in years or days, we converted it to months. For studies that did not report a standard deviation (SD) of mean diagnostic delay, we imputed the SD using the method recommended by Cochrane, which calculates SD using an upper limit, lower limit, and confidence interval [ 6 ]. In studies where the confidence interval was not reported, we calculated SD using the method improved by Wan and colleagues, incorporating the sample size or population [ 22 ].

Categorisation of studies was based on the location or organ involvement of sarcoidosis - pulmonary, extrapulmonary, and systemic. Where sarcoidosis involved only the lungs (defined as changes in hila, mediastina, and the lungs) the location was categorised as pulmonary; where sarcoidosis involved two or more organs the location was categorised as systemic. If only one organ other than the lungs was involved, the location was categorised as extrapulmonary. Health systems were categorised as either gatekeeper (where primary care physicians authorise access to specialist physicians) or non-gatekeeper health systems, based on the dominant health system in the country where the study was conducted. A country was classified as having a gatekeeper system if the system of health financing uniformly used primary care gatekeepers, without the option of self-funding to see specialists, or models of health funding that supported open access to specialists. In countries with diverse health insurance models which may include open access and gatekeepers, such as the USA, an assessment was made for each publication by two authors. Where we could not determine the gatekeeper system used by participants the paper was excluded. We calculated the missing mean age of the study sample when complete data of the study participants was available.

Analysis of diagnostic delay in sarcoidosis

We used an inverse variance weighted random effects model (Der-Simonian-Laird method) to pool mean diagnostic delay [ 6 ]. Sensitivity analyses between studies with estimated SDs and original SDs were conducted. Additionally, we conducted subgroup analyses based on healthcare system type and publication year to investigate possible group differences in diagnostic delay in sarcoidosis. We analysed quantitative data through a meta-synthesis. The alpha level was set at 0.05, and the heterogeneity of meta-analysis estimates was presented using the I 2 statistic. Funnel plots were used to assess the risk of publication bias.

We descriptively analysed and presented a narrative synthesis of the quantitative data from case reports that could not be pooled. Gender difference in diagnostic delay was calculated in case reports where data on sex and delay in diagnosis (months) was available. The distribution of delay in diagnosis in case reports was examined by density plot and Shapiro test ( p  <.05), indicating non-normal distribution; thus, the Mann-Whitney-Wilcoxon test was used to analyse the group differences of delay in diagnosis by sex. All statistical analyses were performed using R version 4.6.2 [ 23 ] and the ‘meta’ package.

Analysis of symptoms, factors, outcomes and experiences associated with diagnostic delay

To investigate the factors associated with diagnostic delay, data on symptoms that changed the diagnosis, and factors related to and outcomes of diagnostic delay were extracted and synthesised using meta-aggregation, for which meanings from qualitative data are identified and aggregated into categories that can be synthesised and analysed [ 24 ]. The broader categorisation of the aggregated data was decided through peer discussion and referral back to the original papers when needed. Additionally, factors linked to pulmonary, extrapulmonary and systemic sarcoidosis were grouped and further analysed.

To our knowledge, none of the included studies reported data on experiences of diagnostic delay in sarcoidosis.

Out of 374 titles identified, we removed 100 duplicates, and screened 274 titles and abstracts. Of those, 67 articles were reviewed at full text and 29 studies were included in the review as shown in Fig.  1 .

Selection flow chart of studies included in the systematic review

Description of included studies

Included studies are summarised in Table  2 and a full data extraction table is presented in Supplementary Table 1 . The 29 included studies comprised 24 non-comparative descriptive studies (including 15 case reports [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], five case series [ 40 , 41 , 42 , 43 , 44 ], two surveys [ 45 , 46 ], and two descriptive cross-sectional studies [ 2 , 47 ]), and five comparative studies (all analytical cross-sectional studies) [ 9 , 48 , 49 , 50 , 51 ]. Twenty-eight of the included studies used non-patient-reported data including clinical reports and retrospective patient registry data, while one used patient-reported data [ 45 ]. In total, there were eleven studies from Europe [ 2 , 9 , 25 , 26 , 33 , 35 , 38 , 42 , 45 , 47 , 48 ], nine from the United States or Canada [ 27 , 29 , 30 , 32 , 34 , 37 , 43 , 44 , 49 ], three from West Asia [ 41 , 46 , 50 ], four from East Asia [ 28 , 31 , 39 , 40 ], one from sub-Saharan Africa [ 36 ], and one from South America [ 51 ]. Various organ involvement of sarcoidosis was reported, including eyes [ 9 ], nasal passages [ 42 ], kidney [ 26 , 27 ], skin [ 28 , 34 ], heart [ 40 , 48 ], nervous system [ 30 , 38 , 44 ], lungs [ 35 , 36 , 37 , 43 ], skeletal muscle [ 33 ], subcutaneous tissue [ 39 ], and systemic or mixed [ 2 , 25 , 29 , 31 , 32 , 41 , 45 , 46 , 49 , 50 , 51 ]. Based on the manual categorisation, thirteen studies examined extrapulmonary sarcoidosis [ 26 , 27 , 28 , 29 , 30 , 32 , 33 , 34 , 39 , 40 , 44 , 47 , 48 ], five examined systemic sarcoidosis [ 9 , 25 , 31 , 38 , 42 ], and four examined pulmonary sarcoidosis [ 35 , 36 , 37 , 43 ]. In seven studies it was not possible to differentiate between pulmonary and non-pulmonary sarcoidosis [ 2 , 41 , 45 , 46 , 49 , 50 , 51 ]. Of the 29 included studies, 18 were from countries with non-gatekeeper health systems (2, 25, 27–33, 3537, 39, 40, 43, 44, 47, 49) and 11 were from countries with gatekeeper health systems [ 9 , 26 , 34 , 38 , 41 , 42 , 45 , 46 , 48 , 50 , 51 ]. Twelve studies reported data on ethnicity or race [ 2 , 25 , 29 , 30 , 31 , 32 , 33 , 36 , 42 , 43 , 49 , 51 ].

In total, a population size of 1531 participants (694 females; 837 males) was included in the review. The mean age was 47.91 years (SD = 5.47), excluding case reports (see below). Overall, participant ages ranged from 9.3 years to 69 years (including case reports).

Results of the quality appraisal

Consensus on the quality appraisal of the included studies is shown in Supplementary Table 2 . After the double-quality appraisal, a consensus was reached by two authors regarding an overall low risk of bias for all studies; therefore, no study was excluded.

Case studies

Twenty case studies comprising 15 case reports (8 females; 7 males) [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ] and five case series [ 40 , 41 , 42 , 43 , 44 ], with 29 participants (22 females, 7 males), were included. The mean age of participants in case report studies was 47.87 years (SD = 14.06 years), with individual age ranging between 26 years [ 25 ] and 69 years [ 27 ]. In the case series, mean age of individuals ranged from 9.3 years [ 41 ] to 44 years [ 42 ].

Of the 20 included case studies, 11 examined extrapulmonary sarcoidosis [ 26 , 27 , 28 , 29 , 30 , 32 , 33 , 34 , 39 , 40 , 44 ], and four each focused on pulmonary [ 35 , 36 , 37 , 43 ] and systemic sarcoidosis [ 25 , 31 , 38 , 42 ]. In the one remaining case study, it was not possible to determine the extent of organ involvement [ 41 ].

In the 15 included case reports, individual diagnostic delay ranged from 0.25 months (0.02 years) [ 39 ] to 96 months (8 years) [ 35 ] and the mean diagnostic delay was 21.73 months. In the five case series, the mean diagnostic delay ranged from 5 months [ 42 ] to 43.5 months [ 43 ].

There was no significant gender difference in delay in diagnosis in case reports ( n  = 15, Mann-Whitney-Wilcoxon test: w = 21.5, p  =.749).

Pooled diagnostic delay in sarcoidosis

The results of the pooled mean diagnostic delay of the five studies [ 2 , 9 , 23 , 41 , 42 ] with an overall sample size of 124 are presented in Fig.  2 . Individual study sample size of these studies ranged from 8 [ 41 , 42 ] to 67 [ 9 ], while the mean diagnostic delay ranged from 5 months [ 42 ] to 23 months [ 9 ]. The pooled diagnostic delay was 7.93 months (95% CI 1.21 to 14.64 months) ( Fig.  2 ) . A funnel plot of the pooled diagnostic delay is presented in Supplementary Fig.  1 . We conducted a sensitivity analysis on SD estimated studies and SD not estimated studies and found no significant difference (between groups difference = 1.06 months, P  =.30) in mean diagnostic delay between the two groups as shown in Supplementary Fig.  2 .

Pooled mean diagnostic delay in sarcoidosis

We could not conduct a subgroup analysis between pulmonary, extrapulmonary and systemic sarcoidosis due to the small number of studies with complete data (mean delay, total number of participants and SD of mean delay) in each group. However, in the included studies, systemic sarcoidosis had the longest mean diagnostic delay at 23.0 months [ 9 ] compared with extrapulmonary sarcoidosis, which had the shortest mean diagnostic delay of 5.0 months [ 42 ].

A subgroup analysis comparing studies ( n  = 5) with different healthcare systems is presented in Supplementary Fig.  3 . There was no significant difference in mean diagnostic delay in countries with gatekeeper healthcare systems when compared with those with non-gatekeeper systems (between groups difference = 0.34 months, P = .56).

We conducted an additional subgroup analysis examining publication year of studies, which showed a significant inter-study difference in diagnostic delay in studies conducted (between groups difference = 16.99 months, P  =.002) (see Supplementary Fig.  4 ). Further analysis examining publication year of the studies (e.g., before 2000 and after 2000) was not feasible due to the small number of studies.

Initial symptoms

Twenty-one studies comprising 15 case reports [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], three case series [ 40 , 42 , 43 ], two cross-sectional studies [ 47 , 49 ] and one survey [ 46 ] reported initial symptoms. Initial symptoms included weight loss [ 29 , 36 , 37 , 41 , 43 ], fatigue or generalised weakness [ 29 , 37 , 40 , 43 ], dyspnoea [ 36 , 40 , 43 ], muscle pain/muscle cramps/general body pain [ 32 , 37 , 40 ], headache [ 38 ], palpitations [ 40 ], nasal obstruction [ 42 ] and a subcutaneous mass [ 39 ] (refer to Supplementary Table 3 ). When aggregated, these symptoms could be categorised as: (1) general symptoms (fever, fatigue, weight loss), (2) organ-specific extrapulmonary symptoms (neurological- nausea, headache, vomiting; cardiac- palpitations; skin - rash, ulcers), and (3) pulmonary symptoms (cough, dyspnoea). Of the initial symptoms, 31.25% (25/80) were general; 55% (44/80) were organ specific and related to extrapulmonary symptoms, while 13.75% (11/80) were pulmonary (see Supplementary Table 3 ).

Initial specialist and treatment/diagnostic centre

Five of the included studies reported the cadre of specialist first consulted, one study each reporting general practitioner [ 29 ], emergency specialist [ 31 ], gynaecologist [ 38 ], oncologist [ 39 ], and neurologist [ 32 ] as the first specialist consulted. Twenty-one studies reported visits to treatment or diagnostic centres including secondary or tertiary hospitals, research centres and university hospitals [ 2 , 9 , 25 , 26 , 27 , 31 , 32 , 33 , 35 , 37 , 38 , 39 , 40 , 41 , 42 , 44 , 47 , 48 , 49 , 50 , 51 ]. Nineteen of these 21 studies reported treatment or diagnosis at multidisciplinary centres [ 2 , 9 , 25 , 26 , 27 , 31 , 32 , 33 , 35 , 37 , 38 , 41 , 42 , 44 , 47 , 48 , 50 , 51 ], and one study each at an institute of oncology [ 39 ] and a research centre [ 49 ].

Symptoms that changed the diagnostic approach

Twelve case studies, containing a total of 13 cases/participants, reported 24 symptoms that changed the diagnostic approach [ 27 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 40 , 43 ]. These symptoms ranged from no response to treatment [ 31 , 36 , 43 ], persistent or increasing shortness of breath/dyspnoea [ 35 , 40 , 43 ], persistent cough [ 35 , 37 ] to worsening hypertension [ 27 ], renal function decline and hypercalcemia [ 27 ] (Supplementary Table 4 ). None of the cross-sectional studies and surveys reported symptoms that changed the diagnostic approach. When aggregated, symptoms that changed the diagnostic approach were categorised into: (1) persistent symptoms (7/24, 29.2%) [ 33 , 35 , 40 , 43 ], (2) new symptoms or signs (7/24, 29.2%) [ 31 , 32 , 38 ], (3) worsening of symptoms (6/24, 25%) [ 27 , 34 , 40 ] and (4) no response to treatment (4/24, 16.6%) [ 31 , 36 , 43 ], as shown in Supplementary Tables 4 and Supplementary Fig.  5 .

Factors related to diagnostic delay

Fifteen case reports [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], three case series [ 40 , 42 , 44 ], two analytical cross-sectional studies [ 9 , 48 ], one survey [ 45 ] and one descriptive cross-sectional study [ 47 ] reported factors that might influence diagnostic delay in sarcoidosis (see Supplementary Table 5 ). Two analytical cross-sectional studies examined association between several factors and diagnostic delay [ 49 , 51 ]. In one study, the presence of pulmonary symptoms was associated with a longer time to diagnosis, whereas the presence of skin symptoms was associated with a shorter time to diagnosis [ 49 ]. People assessed as being at a higher stage on the Scadding scale (radiological scale to measure lung changes; higher stage correlates to greater structural damage in lungs) had a longer time-to-diagnosis compared to people with lower stage features (stage IV vs. stage II, stage III vs. stage 0 or I on chest radiographs) [ 49 ]. One study in Brazil found that misdiagnosis of and treatment for tuberculosis was more likely to be reported among those with a time-to-diagnosis of more than 6 months [ 51 ].

The factors mentioned in the 22 studies were meta-aggregated and the results are shown in Fig.  3 . We categorised these factors into: (1) complex and rare features of sarcoidosis (27/35, 77.1%), (2) healthcare factors (7/35, 20%) and (3) patient-centred factors (1/35, 2.9%). Of these, 77.1% (27/35 factors) were related to complex and rare features of sarcoidosis (category 1), including broad clinical features and differential diagnosis [ 9 , 25 , 26 , 27 , 28 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 40 , 42 , 44 , 47 , 48 ], rare presentation [ 28 , 32 , 34 , 36 , 37 , 38 , 42 ], lack of awareness and rarity of sarcoidosis [ 29 , 30 , 32 , 33 , 40 ], and coexisting disease or comorbidities [ 35 , 38 ]. The 20% (7/35 factors) pertaining to healthcare factors (category 2) included exclusion diagnosis [ 39 ], lack of standard procedure to distinguish sarcoidosis [ 47 ], not using appropriate diagnostic techniques/ relying on chest x-ray [ 45 , 48 ], challenges with biopsy [ 9 , 40 ], and challenges with making a definitive diagnosis in sarcoidosis [ 32 ]. The remaining 2.9% of factors were patient-centred (category 3), which referred to refusal of biopsy (1/35 factors) [ 35 ].

Meta-aggregation results of factors related to diagnostic delay in sarcoidosis

We further analysed these factors by sarcoidosis type (Supplementary Table 6 ). Twenty-two studies reported types of sarcoidosis; of these, 21 studies [ 9 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 42 , 44 , 47 , 48 ] reported factors related to diagnostic delay. Three studies reported five factors of diagnostic delay in pulmonary sarcoidosis. Of these, 80% were categorised as complex and rare features of sarcoidosis (category 1), which included co-existing disease and comorbidities [ 35 ], rare presentations [ 36 , 37 ] and broad clinical features [ 37 ]. The remaining 20% were patient-centred factors, referring to patient’s refusal of a biopsy (category 3) [ 35 ]. Thirteen studies reported twenty factors related to diagnostic delay in extrapulmonary sarcoidosis [ 26 , 27 , 28 , 29 , 30 , 32 , 33 , 34 , 39 , 40 , 44 , 47 , 48 ]. Of these, 75% were linked to complex and rare features of sarcoidosis (category 1), including broad clinical features and differential diagnosis [ 26 , 27 , 28 , 40 , 44 , 47 , 48 ], rare presentation [ 28 , 32 , 34 ] and lack of awareness of sarcoidosis [ 29 , 30 , 32 , 33 , 40 ]. The remaining 25% were categorised as healthcare related (category 2), which included factors relating to healthcare providers [ 48 ] and challenges with diagnostic approach or tools [ 32 , 39 , 40 , 47 ]. Nine factors were mentioned to be linked to diagnostic delay in systemic sarcoidosis [ 9 , 25 , 31 , 38 , 42 ]; eight of these were linked to the complex and rare features of sarcoidosis (category 1); broad clinical features [ 25 , 31 , 38 , 42 ], rare presentation [ 9 , 38 , 42 ], and co-existing disease [ 38 ]. One factor was linked to healthcare (category 2): challenges with diagnostic approach and tool, described by the authors of the paper as limited number of patients amenable to lymph node biopsy [ 9 ].

Outcomes related to diagnostic delay

Sixteen studies described the outcomes of diagnostic delay, including 11 case reports [ 26 , 27 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], two case series [ 40 , 44 ], two analytical cross-sectional studies [ 48 , 51 ], and one survey [ 45 ]. The survey and analytical cross-sectional studies did not use statistical methods to examine the relationship between independent variables and diagnostic delay; however, they reported descriptive or comparative results of the outcomes of diagnostic delay. One study described incorrect diagnoses that were provided instead of sarcoidosis, including tuberculosis, lung cancer, rheumatic fever, Hodgkin’s lymphoma, pneumonia, and patients simulating the symptoms [ 45 ]. One study reported irreversible deterioration of cardiac function (6/10 cases) and high mortality (5/10 cases) in people with a late diagnosis of sarcoidosis [ 48 ], and another study reported poor lung function in people with a late diagnosis [ 51 ].

While case reports or case studies are not designed to assess the association between two variables, we analysed their data using meta-aggregation as shown in Supplementary Tables 7 and Fig.  4 . Thirteen case studies, including 11 case reports [ 26 , 27 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ] and two case series [ 40 , 44 ], described outcomes from 26 cases. We aggregated the outcomes into: (1) incorrect diagnosis, (2) incorrect treatment and (3) complications/progression of the condition. Incorrect diagnosis (category 1) was reported in 38.5% (10/26 cases), including xanthogranulomatous pyelonephritis [ 26 ], monoclonal gammopathy of undetermined significance [ 27 ], tuberculosis [ 31 , 36 ], deep tissue infection [ 34 ], bronchitis [ 35 ], respiratory infection [ 37 ], tachycardia and heart block [ 40 ], and multiple sclerosis [ 44 ]. Incorrect treatment (category 2) was reported in 34.6% (9/10 cases), consisting of nephrectomy [ 26 ], anti-tuberculosis agents [ 31 , 36 ], antibiotics [ 34 , 35 , 37 ] and excision of mass [ 39 ]. Complications/progression of symptoms or the condition (category 3) was reported in 26.9% (7/10 cases) of the cases. These included renal failure [ 27 ], seizure [ 32 ], weakness of the extremities [ 33 ], infection [ 34 ], dyspnoea and oxygen therapy [ 35 ], headache, vomiting and blurred vision [ 38 ], dyspnoea and haemoptysis [ 40 ].

Meta-aggregation of outcomes of diagnostic delay in case studies

People’s experiences related to diagnostic delay

We did not identify any studies, including qualitative, that examined people’s experiences of diagnostic delay in our systematic search.

Using data from the 29 studies included in this review, we were able to present a pooled analysis of diagnostic delay in all types of sarcoidosis to describe factors that are related to and associated with diagnostic delay, and the outcomes for people living with sarcoidosis. Pooled mean diagnostic delay for all types of sarcoidosis was 7.93 months (95% CI 1.21 to 14.64 months), a similar range to delays described for other chronic inflammatory diseases, including inflammatory bowel disease [ 52 ]. The overall sample pool of this study consisted of more males than females (54.7% vs. 45.3%). No difference in delay in diagnosis was found between males and females based on the analysis conducted on case reports. The high number of single-person case studies on misdiagnosis attests to the size of the diagnostic challenge for the clinician. Several factors may influence diagnostic delay of sarcoidosis, including the clinical characteristics of the condition, prevalence, different types/presentation of the condition, clinicians’ and patients’ awareness of the condition, and the availability of diagnostic tests.

The present review found complex and rare features of sarcoidosis, healthcare factors, and patient-centred factors may contribute to diagnostic delay in all types of sarcoidosis. In some studies included in the review, associations were found between pulmonary symptoms and higher Scadding scores, and prolonged diagnostic delay of sarcoidosis. The presence of pulmonary symptoms that may be attributable to various health conditions (common flu, pneumonia, bronchitis, asthma, emphysema, and lung cancer) create challenges for healthcare providers working to narrow down the health condition and differentiate between possible causes of pulmonary symptoms. In these cases, healthcare providers may first choose to investigate more common causes of pulmonary symptoms and pursue a diagnostic approach that excludes the most common causes through minimal testing, which is cost effective.

The review also revealed healthcare factors (exclusion diagnosis, challenges with obtaining a biopsy and lack of standard procedure to distinguish sarcoidosis) may lead to diagnostic delay. Difficulties with access to medical resources needed to conduct a biopsy (availability of clinicians and medical facilities) may cause delay in the definitive diagnosis of sarcoidosis through extending the time between suspicion and confirmation of diagnosis. Identifying the difference between suspicion and confirmation of diagnosis can provide further insights into the depth of the impact on diagnostic delay associated with healthcare factors.

Diagnostic delay due to misdiagnosis of tuberculosis was also identified in this review, highlighting the similarity of the two conditions and that differentiating between them is crucial for initiating the correct treatment, as treatment of sarcoidosis involves immunosuppression. In countries with a high prevalence of tuberculosis, it is understandable that clinicians may initially suspect tuberculosis. A misdiagnosis of tuberculosis has implications for the individual, their families and carers, and the use of medical resources, signalling the need for a careful and methodical approach in diagnosis. Once a clinician has made a diagnosis, it is natural to attribute the constellation of symptoms and signs of a rare disease to the identified cause (misdiagnosed condition), until clear evidence arises to disprove the current diagnosis.

Both acute and chronic presentation of sarcoidosis may influence the diagnostic delay. Acute sarcoidosis may follow acute onset with more typical features and radiological findings (hilar adenopathy in chest x-ray). Chronic sarcoidosis has insidious onset and may mimic other disorders (signs and symptoms from multiple systems); therefore, chronic sarcoidosis may present additional challenges for diagnosis of sarcoidosis. The present review did not study the difference in diagnostic delay between acute and chronic sarcoidosis due to limited data. Analyses of sarcoidosis location and factors related to diagnostic delay revealed similar findings, in which most reported factors were linked to complex and rare features, regardless of the location of sarcoidosis. Raising clinicians’ awareness of the complex clinical presentations of all types of sarcoidosis, including rare presentations, may assist in expediting diagnosis.

While none of the included studies used quantitative methods to examine outcomes of diagnostic delay, we used meta-aggregation to extract and examine outcomes described in case reports and case series which revealed incorrect diagnosis, incorrect treatment, and complications/progression of the condition as outcomes of diagnostic delay of sarcoidosis. This accords with findings from a recent review of diagnostic delay in myositis where outcomes including misdiagnoses, progression of symptoms, incorrect treatment, and early discharge were reported [ 53 ]. These outcomes align with people’s experiences of diagnostic delay recently described [ 54 ], signalling the need for improved awareness of sarcoidosis and a better understanding of its diagnosis and treatment.

As in our previous study examining diagnostic delay of myositis, where we did not find any studies examining people’s experiences of diagnostic delay [ 53 ], we did not find research examining experiences of diagnostic delay of sarcoidosis. We believe that further exploration of people’s experiences from symptom onset until diagnosis may assist in understanding these experiences and factors that may impact and influence diagnosis and its delay in sarcoidosis. This information may then be used to inform strategies aimed at reducing the undiagnosed period, including raising awareness and the development of clinical reasoning tools to distinguish when clinicians might consider re-evaluation of an existing diagnosis and the presence of a rare disease.

Despite the lack of studies examining people with sarcoidosis’ experiences of diagnostic delay, a recent commentary describes people with sarcoidosis’ experiences of misdiagnoses [ 54 ]. One person described frustration at ‘being dismissed’ and not listened to by their clinician, an experience that has also been described by people with multiple sclerosis seeking a diagnosis [ 55 ]. All of those interviewed for the article highlighted ongoing pain and discomfort from symptoms pre- and post-diagnosis as greatly impacting their lives, aligning with evidence of the negative impact that sarcoidosis has on people’s quality of life [ 56 ].

Diagnostic delay can create a sense of uncertainty and, in many cases, escalating symptoms, as found in research examining people’s experiences with multiple sclerosis [ 55 ], placing them in a stressful state of ‘not knowing”. Delayed diagnosis of childhood illnesses has consequences for both children and their families, including anxiety, frustration and stress, and fear of future reproduction due to ill-defined genetic risk [ 57 ]. Hospitalisation and surgical interventions related to rare diseases are more frequent among people who experience a delayed diagnosis [ 58 ]. Research examining experiences of hereditary angioedema found that inappropriate treatments were ineffective and at times, exacerbated the underlying condition [ 59 ]. For some patients, symptoms were attributed to psychological reasons and due to this, some stopped seeking medical care despite experiencing severe symptoms [ 59 ]. Attribution of rare disease symptoms to psychological or psychiatric reasons, and treatment in line with this is not uncommon; [ 57 , 58 , 59 ] however the impact of a rare disease on individuals’ mental health has important implications for the treatment and care of people with these health conditions [ 59 ].

Delay in diagnosis of sarcoidosis can cause impaired physical function, pain, reduced capacity to work, and strain on personal relationships, leading to a reduction in quality of life and the ability to engage in pleasurable activities, which in turn can have negative emotional consequences that impact wellbeing [ 60 ]. A survey of the treatment priorities of people with sarcoidosis found that they most valued quality of life and functionality and concluded that psychological support was key to their wellbeing [ 61 ]. Unfortunately, being able to discuss issues and concerns about sarcoidosis with clinician(s) cannot be realised until a diagnosis is received.

There is a paucity of evidence about the patient experience of diagnostic delay in sarcoidosis and factors related to this. Diagnosis of sarcoidosis can take a long time, during which the impacts on the lives of people living with sarcoidosis can be substantial, including receiving incorrect diagnoses and treatment, and suffering unfavourable outcomes. Further studies examining factors that contribute to diagnostic delay in sarcoidosis, and people’s experiences from symptom onset to diagnosis, are crucial in determining target areas for clinicians, policy-makers and consumer advocacy groups. With this further knowledge, we may develop strategies, training activities and awareness-raising programs that expedite diagnosis and improve outcomes for people living with sarcoidosis.

Strengths and limitation

The main strength of this review is inclusion of the current evidence of diagnostic delay in all types of studies (including qualitative and quantitative studies) which provided clear insight into the status of diagnostic delay, its factors, and consequences. This systematic review identified a lack of qualitative studies examining patients’ experience of diagnostic delay in sarcoidosis. The main limitation of the present systematic review is the low number of study samples used in pooling of the diagnostic delay ( n  = 124 over 5 studies). The lack of available data on health specialists, clinics, acute or chronic presentation of sarcoidosis, and the period between suspected and confirmed diagnosis limited the possibility of analysing the difference in diagnostic delay in various settings. Lastly, the analysis of case reports may reflect features of chronic sarcoidosis with complex features due to publication bias- tendency to publish rare and interesting cases.

Data availability

All data relevant to the study is available in the supplementary materials. A detailed extracted data table can be accessed via figtree repository (via DOI: https://doi.org/10.6084/m9.figshare.24431275 ).

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This work was supported by “Missed opportunities in clinical practice: Tools to enhance healthcare providers’ awareness and diagnosis of rare diseases in Australia” a project funded by the Commonwealth represented by Department of Health Australia [ID 4-G5ZN0T7]. Sponsors or funding officials were not involved in any part of the review including protocol development, data selection, synthesis, reporting and publishing of the results.

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Tergel Namsrai, Anne Parkinson, Dianne Gregory, Elaine Kelly & Jane Desborough

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AP, CP, JD, EK, DG, and MC conceptualised the study and supported the study methodology. TN, CP, AP, and JD conducted the data collection and analysis. TN drafted the original manuscript. JD, AP, CP, MC, DG, and EK reviewed and edited the manuscript.

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Namsrai, T., Phillips, C., Parkinson, A. et al. Diagnostic delay of sarcoidosis: an integrated systematic review. Orphanet J Rare Dis 19 , 156 (2024). https://doi.org/10.1186/s13023-024-03152-7

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Received : 23 March 2023

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DOI : https://doi.org/10.1186/s13023-024-03152-7

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Mobiluncus   curtisii Bacteremia: Case Study and Literature Review

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Background: There are few reports of bacteremia caused by Mobiluncus   curtisii in the literature. We present a review of the literature in addition to a case study. Method: We describe the case of an 82-year-old patient who underwent gastrointestinal surgery and subsequently presented with dehydration, nausea, and hyperkalemia secondary to diarrhea. Further clinical work included blood cultures, and the patient was started empirically on piperacillin/tazobactam. Results: After five days, the blood culture bottle showed growth of a gram-variable, curved rod-shaped organism. After culture under anaerobic conditions on sheep blood agar, the organism was identified as Mobiluncus   curtisii by MALDI-TOF mass spectrometry and enzymatic technology. A review of the literature reveals five additional cases of Mobiluncus   curtisii bacteremia. Conclusions: This is the sixth case in the literature describing Mobiluncus species bacteremia. This organism is rarely identified in blood culture and is most often thought of in the context of bacterial vaginosis. However, the reported cases of bacteremia show gastrointestinal symptoms and presumed gastrointestinal source of infection. The pathogenesis of infection of this organism requires further investigation.

1. Introduction

Mobiluncus species are gram variable curved rod-shaped organisms. They are non-spore-forming, motile, with somewhat tapered ends, and may present as pairs with a “gullwing” appearance when two organisms are seen in a pair with tapered ends resembling a seagull shape. In the literature, Mobiluncus species are most commonly discussed in relation to their identification in gynecologic infections, in particular, bacterial vaginosis. However, the role of this organism in bacterial vaginosis remains poorly understood. A puzzling finding is that even with the knowledge that this organism is well documented to be resistant to metronidazole, metronidazole remains a common and effective treatment for bacterial vaginosis. For an organism that is resistant to metronidazole, the treatment of bacterial vaginosis with metronidazole and its subsequent resolution would suggest that Mobiluncus is not the only organism involved in bacterial vaginosis, and there are likely many complex variables that lead to Mobiluncus species identification in association with genitourinary infections. Further research has suggested that although most commonly associated with genital infections, it may be a colonizer of the gastrointestinal tract. This is supported by cases described in a review of the literature presented here and based upon studies that tested rectal samples of patients with and without bacterial vaginosis. It is rare to isolate Mobiluncus species from an extragenital site, and here we present a case of Mobiluncus bacteremia in an 82-year-old female and a review of the literature regarding Mobiluncus bacteremia. Our patient is the sixth reported case in the literature of Mobiluncus bacteremia, helping to expand upon the limited literature surrounding this organism in the context of isolating it in blood cultures. Increased awareness of this organism in blood cultures is required to elicit more cases and to form meaningful conclusions about the virulence, origin, and clinical presentation for patients presenting with Mobiluncus bacteremia.

2. Clinical Presentation

Our patient is an 82-year-old female with a history of diabetes mellitus type 2, hypertension, coronary artery disease, and chronic kidney disease. She had a prolonged hospitalization three months prior to the reported bacteremia due to a small bowel bleed caused by angiodysplasia. She underwent a small bowel resection procedure with ileostomy formation followed by multiple recurrent gastrointestinal operations due to post-operative complications. More recently, she presented to the Emergency Department with complaints of diarrhea and dehydration three months after her hospitalization for the small bowel resection. After initial emergency room testing, she was transferred to a nearby hospital due to an initial finding of hyperkalemia. Of note, two initial blood cultures were drawn in the Emergency Department. After transfer to the hospital, along with the hyperkalemia, the patient was noted to have laboratory findings consistent with acute tubular necrosis/acute renal failure presumably due to severe volume depletion as a result of ileostomy/diarrheal loss. Rehydration with intravenous fluids normalized her renal function. She was discharged nine days after an emergency department visit and hospital admission. Importantly, the prior bowel resection procedure left the patient with a large midline, recovering incision, which was noted to be healing with a wound vac in place at the time of this hospital admission. Urinalysis at the hospital showed many bacteria and a large amount of blood. Computed tomography (CT) imaging showed findings consistent with cystitis, and the patient was empirically started on piperacillin/tazobactam. The presumption was that the patient was septic from a urinary tract infection.

3. Materials and Methods

The blood cultures collected at the Emergency Room on initial presentation were documented as a gram-positive rod on Gram’s stain. The Gram’s stain result was faxed and called to the hospital five days into the admission. The blood culture bottle was then received a day after the Gram’s stain result was called at the University of Minnesota Infectious Diseases Diagnostic Lab as an anaerobe referral for definitive identification. The organism was cultured on a blood agar plate under anaerobic conditions ( Figure 1 a), and the colony Gram’s stain showed gram-variable, curved rod-shaped organisms ( Figure 1 b). The organism was identified as Mobiluncus curtisii by MALDI-TOF mass spectrometry (Vitek MS, bioMérieux, Marcy l’Etoile, France) at a confidence level of 99.9% and as Mobiluncus curtisii by enzyme technology using the RapID™ ANAII system for anaerobic bacteria (ThermoFisher Scientific, Waltham, MA, USA) at a probability of >99.9%. A limitation of our study is that data from sequencing are not available, as it is not routinely performed for identification in our laboratory. Therefore, it is highly probable, but not 100% certain, that this organism was correctly identified as Mobiluncus curtisii by two separate testing modalities.

( a ) Image of the sheep blood agar plate grown in anaerobic conditions showing colorless, translucent, smooth, convex colonies after 5 days of incubation. ( b ) Image of Gram’s stain at 1000× magnification, with oil immersion. The organism was curved and rod-shaped, gram-variable, and a predominant gram-negative staining pattern was displayed here.

4. Discussion

The Mobiluncus genus is subdivided into two species, Mobiluncus mulieris and Mobiluncus curtisii (which is even further subdivided into subspecies Mobiluncus curtisii subsp. curtisii and Mobiluncus curtisii subsp. holmesii ) [ 1 ]. Mobiluncus curtisii subspecies curtisii is typically a gram-variable, curved rod-shaped, non-spore-forming, motile organism with tapered ends, occurring singly or in pairs with a “gullwing” appearance. Clusters of two to six flagella which are longer than the bacterial cells, have been observed on electron micrographs. Although the Gram’s stain reactions of the curved, rod-shaped organisms are reported as variable, electron micrographs reveal multilayered gram-positive cell walls lacking an outer membrane. Even in this case, the initial callback stated that the organism was gram-positive, whereas after identification at the University of Minnesota, the organism was identified as gram-variable, but as seen in Figure 1 b, shows a predominantly gram-negative type staining with only rare gram-positive organisms. Gardnerella vaginalis , another gram-variable organism, also has a multilayered wall. The thinness of the peptidoglycan layer may explain the tendency of the curved rod-shaped organisms to stain gram-negative. Based upon observations of this organism in culture, young cultures tended to show more gram-positive staining [ 2 ]. The apparent absence of an outer membrane suggests that Mobiluncus species more closely resemble gram-positive organisms than gram-negative organisms. This conclusion is supported by reports that these organisms are resistant to colistin and nalidixic acid and are susceptible to penicillin, ampicillin and vancomycin. Hydroxy fatty acids, commonly found in gram-negative cell walls, are absent in these organisms [ 2 ]. Moreover, DNA sequencing places the organism in the family Actinomycetaceae, which is a family of gram-positive organisms [ 3 ].

Mobiluncus species have been shown to be associated with isolates from patients with bacterial vaginosis [ 4 ]. Because Mobiluncus curtisii and Mobiluncus mulieris do not produce putrescine or cadaverine in peptone-starch-dextrose broth supplemented with lysine and ornithine, these species are not the source of the amine odor associated with bacterial vaginosis [ 2 ]. One published study by author Holst [ 5 ] showed that Mobiluncus species were isolated from 97% of patients with bacterial vaginosis. A later study by Schwebke et al. [ 6 ] showed a similar result using polymerase chain reaction (PCR) that Mobiluncus species were identified in 84.5% of women with bacterial vaginosis and only 38% of women without bacterial vaginosis infection. Moreover, Mobiluncus curtisii, specifically, was rarely detected in women without bacterial vaginosis, and it was found in 65.3% of women with bacterial vaginosis [ 7 ]. The pathogenic role of Mobiluncus is still unclear in bacterial vaginosis since Mobiluncus species are usually resistant to metronidazole, which is an effective treatment for most cases of bacterial vaginosis [ 6 ]. Holst [ 5 ] also showed, of those women with bacterial vaginosis, 45 to 62% had Mobiluncus species isolated from concurrent rectal samples, whereas Mobiluncus was isolated from only 10 to 14% of the rectums of women without bacterial vaginosis.

Additionally, Holst [ 5 ] reported that 5–11% of men and children had Mobiluncus species isolated from rectal samples. These findings caused researchers to deliberate if this organism resides in the gastrointestinal tract and may not be primarily thought of as a genital bacterium. If the intestinal tract is the main reservoir for Mobiluncus species, it could be presumed that an acute abdominal problem may allow dissemination and initiate bacteremia. Alternatively, as a possibility, in this case, the bacteria may have spread from the genitourinary space or the ileostomy site to nearby damaged skin or the relatively nearby large midline surgical incision. Given the extensive gastrointestinal surgeries and healing ileostomy site, the presumed source, in this case, is gastrointestinal; however, travel from the genitourinary space to nearby damaged epithelium cannot be entirely ruled out.

Extragenital infection by Mobiluncus is rare and has been reported in breast abscesses and bacteremia [ 1 ]. To our knowledge, this is only the sixth case of Mobiluncus bacteremia reported in the literature ( Table 1 ). Four patients, including ours, had Mobiluncus curtisii identified. Of the five cases of Mobiluncus bacteremia reported in the literature, four cases were female. The average age of the reported patients, including our case, is 51 years, with a range from 35 years to 82 years. Two cases of Mobiluncus bacteremia showed life-threatening (severe hypotension) or fatal infections. One patient diagnosed with Mobiluncus bacteremia did not survive, related to a massive intracerebral hemorrhage of unknown cause. One patient had no reported comorbidities suggesting that this unusual bacteremia can affect people who are presumably immunocompetent. Most of the reported cases presented with fever, and all cases had some report of gastrointestinal disturbances, including nausea, diarrhea, vomiting, or abdominal pain. The presumed origin, based upon the case reports of the bacteremia, was the gastrointestinal tract in four patients, including this patient [ 8 , 9 , 10 ], with the other two sources presumed to be uterine [ 11 ] and unknown [ 1 ]. Treatment with an antibiotic led to full recovery in all but one patient. In our case, the patient was treated empirically with piperacillin/tazobactam for a presumed urinary tract infection. The only organism identified by microbiology culture was on the blood culture from the Emergency department, which was identified as Mobiluncus curtisii by the Infectious Diseases Diagnostic Lab at the University of Minnesota. In the reported cases, the blood culture bottle signaled a positive culture in as little as 24 h to as much as 9 days; this may be related to bacterial load in each individual. The person with Mobiluncus bacteremia who did not recover had a positive blood culture after 5 days, which would not support a correlation between the time to a positive culture and clinical course. However, the patient who presented with severe hypotension had a positive blood culture signal after 24 h of incubation, so there may be a relationship between clinical presentation and time to positive culture for this organism. Our understanding of this relationship will be improved as more case reports are published. For those cases with reports of antibiotic resistance, most showed resistance to metronidazole, consistent with the literature and are susceptible to many different antibiotics. The case of Mobiluncus bacteremia caused by Mobiluncus mulieris was sensitive to metronidazole, consistent with what is reported in the literature. Interestingly, three of the five reported cases had metabolic panels which showed transaminitis, and one patient even presented with jaundice and hepatomegaly. This could indicate that Mobiluncus species may cause liver injury. As more cases continue to be reported in the literature, our ability to draw meaningful conclusions regarding infection with this organism will improve tremendously.

Clinical and laboratory features of reported Mobiluncus bacteremia cases.

WBC, peripheral blood white blood cell count (× 109/L); Plt, platelet count (× 109/L); Hgb, hemoglobin concentration (g/dL). S, sensitive; R, resistant; NK, not known.

The pathogenesis of infection with and virulence factors of Mobiluncus curtisii are still not completely understood. One study, by author Zeng [ 12 ], showed that in the Mobiluncus curtisii genome, there is a genomic fragment encoding a 25 kDa pore-forming toxin, the CAMP factor, which is known to be involved in the synergistic lysis of erythrocytes, namely the CAMP reaction. Additionally, another study by Menolascina et al. [ 13 ] suggested that both Mobiluncus curtisii and Mobiluncus mulieris cells have the capacity to adhere, mediated by adhesin, in the absence of glucose or mannose. Lastly, Taylor-Robinson et al. [ 14 ] showed that the centrifuged supernatants of cultures of Mobiluncus curtisii and Mobiluncus mulieris had a toxic effect on epithelial cells, corroborated by the Menolascina et al. group. These factors taken together, in the appropriate growth conditions, could allow Mobiluncus curtisii to adhere to and destroy epithelial cells allowing entry of the organism into the bloodstream from a source of colonization, either the gastrointestinal tract or the genitourinary tract. As more cases of Mobiluncus species bacteremia are published we will begin to understand more of the ecology and the pathogenesis of infection with this organism.

5. Conclusions

Our case is only the sixth case reported in the literature describing Mobiluncus species bacteremia. Mobiluncus curtisii is rarely identified in blood culture and is most often thought of in the context of bacterial vaginosis. However, the patients with Mobiluncus bacteremia most often present with gastrointestinal symptoms including diarrhea, abdominal pain, and transaminitis, and the gastrointestinal tract is presumed to be the source of infection. The pathogenesis of infection with this organism requires further investigation. Continued attention to this organism will inevitably lead to new case reports and further understanding of this rarely reported bacteremia with Mobiluncus bacterial species.

Acknowledgments

Infectious Diseases Diagnostic Laboratory (IDDL) staff at the University of Minnesota Medical Center.

Author Contributions

Conceptualization, C.A. and P.F.; writing—original draft preparation, C.A.; writing—review and editing, C.A. and P.F. All authors have read and agreed to the published version of the manuscript.

This research received no external funding.

Informed Consent Statement

General informed consent was obtained from all subjects involved in the study.

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Conflicts of interest.

The authors declare no conflict of interest.

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