A Guide to Evidence Synthesis: 4. Write a Search Strategy

  • Meet Our Team
  • Our Published Reviews and Protocols
  • What is Evidence Synthesis?
  • Types of Evidence Synthesis
  • Evidence Synthesis Across Disciplines
  • Finding and Appraising Existing Systematic Reviews
  • 0. Develop a Protocol
  • 1. Draft your Research Question
  • 2. Select Databases
  • 3. Select Grey Literature Sources
  • 4. Write a Search Strategy
  • 5. Register a Protocol
  • 6. Translate Search Strategies
  • 7. Citation Management
  • 8. Article Screening
  • 9. Risk of Bias Assessment
  • 10. Data Extraction
  • 11. Synthesize, Map, or Describe the Results
  • Evidence Synthesis Institute for Librarians
  • Open Access Evidence Synthesis Resources

Video: Databases and search strategies (3:40 minutes)

Writing a Search Strategy

It is recommended that you work with a librarian to help you design comprehensive search strategies across a variety of databases. Writing a successful search strategy takes an intimate knowledge of bibliographic databases.  

Using Boolean logic is an important component of writing a search strategy: 

3 Venn diagrams displaying the differences between the Boolean operators AND, OR, and NOT. Using AND narrows a search by requiring that both terms (puppy and kitten) be included in the results. Using OR broadens a search by requiring either term (puppy or kitten) be included in the results. Using NOT excludes just one term (kitten) so that included results only mention puppy and any results that mention kitten are excluded.

Evidence Synthesis Search Strategy Examples

Agriculture Example: 

Nutrition Example: 

Search Strategy Template and Filters

If you want to exclude animal studies from your search results, you may add a "human studies filter" to the end of your search strategy. This approach works best with databases that use Medical Subject Headings (MeSH) or other controlled vocabulary.

See Appendix 2 at the end of this published search strategy for an example of a human studies filter in a MEDLINE(Ovid) search strategy.

Line 13 searches for all animal studies, and then line 14 searches for only the full search results in line 12, NOT including any of the animal studies from line 13 (#12 NOT #13).

Add the following lines to the end of your search strategy to filter for randomized controlled trials. These are "validated search filters" meaning they have been tested for sensitivity and specificity, and the results of those tests have been published as a scientific article. The ISSG Search Filters Resource provides validated search filters for many other study design types. 

Highly Sensitive MEDLINE (via PubMed) Filter from Cochrane  

(randomized controlled trial [pt] OR controlled clinical trial [pt] OR randomized [tiab] OR placebo [tiab] OR drug therapy [sh] OR randomly [tiab] OR trial [tiab] OR groups [tiab])

Highly Sensitive MEDLINE (OVID) Filter from Cochrane 

((randomized controlled trial.pt. or controlled clinical trial.pt. or randomized.ab. or placebo.ab. or drug therapy.fs. or randomly.ab. or trial.ab. or groups.ab.) not (exp animals/ not humans.sh.)) ​

CINAHL Filter from Cochrane 

TX allocat* random* OR (MH "Quantitative Studies") OR (MH "Placebos") OR TX placebo* OR TX random* allocat* OR (MH "Random Assignment") OR TX randomi* control* trial* OR TX ( (singl* n1 blind*) OR (singl* n1 mask*) ) OR TX ( (doubl* n1 blind*) OR (doubl* n1 mask*) ) OR TX ( (tripl* n1 blind*) OR (tripl* n1 mask*) ) OR TX ( (trebl* n1 blind*) OR (trebl* n1 mask*) ) OR TX clinic* n1 trial* OR PT Clinical trial OR (MH "Clinical Trials+")

PsycINFO Filter from ProQuest:

SU.EXACT("Treatment Effectiveness Evaluation") OR SU.EXACT.EXPLODE("Treatment Outcomes") OR SU.EXACT("Placebo") OR SU.EXACT("Followup Studies") OR placebo* OR random* OR "comparative stud*" OR  clinical NEAR/3 trial* OR research NEAR/3 design OR evaluat* NEAR/3 stud* OR prospectiv* NEAR/3 stud* OR (singl* OR doubl* OR trebl* OR tripl*) NEAR/3 (blind* OR mask*)

Web Of Science (WoS) Filter from University of Alberta - Not Validated

TS= clinical trial* OR TS=research design OR TS=comparative stud* OR TS=evaluation stud* OR TS=controlled trial* OR TS=follow-up stud* OR TS=prospective stud* OR TS=random* OR TS=placebo* OR TS=(single blind*) OR TS=(double blind*)

Scopus Filter from Children's Mercy Kansas City

 Copy/paste into 'advanced search':

TITLE-ABS-KEY((clinic* w/1 trial*) OR (randomi* w/1 control*) OR (randomi* w/2 trial*) OR (random* w/1 assign*) OR (random* w/1 allocat*) OR (control* w/1 clinic*) OR (control* w/1 trial) OR placebo* OR (Quantitat* w/1 Stud*) OR (control* w/1 stud*) OR (randomi* w/1 stud*) OR (singl* w/1 blind*) or (singl* w/1 mask*) OR (doubl* w/1 blind*) OR (doubl* w/1 mask*) OR (tripl* w/1 blind*) OR (tripl* w/1 mask*) OR (trebl* w/1 blind*) OR (trebl* w/1 mask*)) AND NOT (SRCTYPE(b) OR SRCTYPE(k) OR SRCTYPE(p) OR SRCTYPE(r) OR SRCTYPE(d) OR DOCTYPE(ab) OR DOCTYPE(bk) OR DOCTYPE(ch) OR DOCTYPE(bz) OR DOCTYPE(cr) OR DOCTYPE(ed) OR DOCTYPE(er) OR DOCTYPE(le) OR DOCTYPE(no) OR DOCTYPE(pr) OR DOCTYPE(rp) OR DOCTYPE(re) OR DOCTYPE(sh))

Sources and more information:

Pre-generated queries in Scopus for the UN Sustainable Development Goals

Pre-written SDG search strategies available in Scopus 

Scopus, a database of multidisciplinary research, provides pre-written search strategies to capture articles on topics about each of the 17 United Nations Sustainable Development Goals  (SDGs). To access these SDG search strategies in Scopus: 

More about the Sustainable Development Goals: 

" The 2030 Agenda for Sustainable Development,  adopted by all United Nations Member States in 2015, provides a shared blueprint for peace and prosperity for people and the planet, now and into the future. At its heart are the 17 Sustainable Development Goals (SDGs), which are an urgent call for action by all countries - developed and developing - in a global partnership. They recognize that ending poverty and other deprivations must go hand-in-hand with strategies that improve health and education, reduce inequality, and spur economic growth – all while tackling climate change and working to preserve our oceans and forests."

Source:  https://sdgs.un.org/goals 

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Literature searching explained

Develop a search strategy.

A search strategy is an organised structure of key terms used to search a database. The search strategy combines the key concepts of your search question in order to retrieve accurate results.

Your search strategy will account for all:

Each database works differently so you need to adapt your search strategy for each database. You may wish to develop a number of separate search strategies if your research covers several different areas.

It is a good idea to test your strategies and refine them after you have reviewed the search results.

How a search strategy looks in practice

Take a look at this example literature search in PsycINFO (PDF) about self-esteem.

The example shows the subject heading and keyword searches that have been carried out for each concept within our research question and how they have been combined using Boolean operators. It also shows where keyword techniques like truncation, wildcards and adjacency searching have been used.

Search strategy techniques

The next sections show some techniques you can use to develop your search strategy.

Skip straight to:

Searching with subject headings

Citation searching

Choose search terms.

Concepts can be expressed in different ways eg “self-esteem” might be referred to as “self-worth”. Your aim is to consider each of your concepts and come up with a list of the different ways they could be expressed.

To find alternative keywords or phrases for your concepts try the following:

When you've done this, you should have lists of words and phrases for each concept as in this completed PICO model (PDF) or this example concept map (PDF).

As you search and scan articles and abstracts, you may discover different key terms to enhance your search strategy.

Using truncation and wildcards can save you time and effort by finding alternative keywords.

Search with keywords

Keywords are free text words and phrases. Database search strategies use a combination of free text and subject headings (where applicable).

A keyword search usually looks for your search terms in the title and abstract of a reference. You may wish to search in title fields only if you want a small number of specific results.

Some databases will find the exact word or phrase, so make sure your spelling is accurate or you will miss references.

Search for the exact phrase

If you want words to appear next to each other in an exact phrase, use quotation marks, eg “self-esteem”.

Phrase searching decreases the number of results you get and makes your results more relevant. Most databases allow you to search for phrases, but check the database guide if you are unsure.

Truncation and wildcard searches

You can use truncated and wildcard searches to find variations of your search term. Truncation is useful for finding singular and plural forms of words and variant endings.

Many databases use an asterisk (*) as their truncation symbol. Check the database help section if you are not sure which symbol to use. For example, “therap*” will find therapy, therapies, therapist or therapists. A wildcard finds variant spellings of words. Use it to search for a single character, or no character.

Check the database help section to see which symbol to use as a wildcard.

Wildcards are useful for finding British and American spellings, for example: “behavio?r” in Medline will find both behaviour and behavior.

There are sometimes different symbols to find a variable single character. For example, in the Medline database, “wom#n” will find woman and also women.

Use adjacency searching for more accurate results

You can specify how close two words appear together in your search strategy. This can make your results more relevant; generally the closer two words appear to each other, the closer the relationship is between them.

Commands for adjacency searching differ among databases, so make sure you consult database guides.

In OvidSP databases (like Medline), searching for “physician ADJ3 relationship” will find both physician and relationship within two major words of each other, in any order. This finds more papers than "physician relationship".

Using this adjacency retrieves papers with phrases like "physician patient relationship", "patient physician relationship", "relationship of the physician to the patient" and so on.

Database subject headings are controlled vocabulary terms that a database uses to describe what an article is about.

Watch our 3-minute introduction to subject headings video . You can also  View the video using Microsoft Stream (link opens in a new window, available for University members only).

Using appropriate subject headings enhances your search and will help you to find more results on your topic. This is because subject headings find articles according to their subject, even if the article does not use your chosen key words.

You should combine both subject headings and keywords in your search strategy for each of the concepts you identify. This is particularly important if you are undertaking a systematic review or an in-depth piece of work

Subject headings may vary between databases, so you need to investigate each database separately to find the subject headings they use. For example, for Medline you can use MeSH (Medical Subject Headings) and for Embase you can use the EMTREE thesaurus.

SEARCH TIP: In Ovid databases, search for a known key paper by title, select the "complete reference" button to see which subject headings the database indexers have given that article, and consider adding relevant ones to your own search strategy.

Use Boolean logic to combine search terms

Boolean operators (AND, OR and NOT) allow you to try different combinations of search terms or subject headings.

Databases often show Boolean operators as buttons or drop-down menus that you can click to combine your search terms or results.

The main Boolean operators are:

OR is used to find articles that mention either of the topics you search for.

AND is used to find articles that mention both of the searched topics.

NOT excludes a search term or concept. It should be used with caution as you may inadvertently exclude relevant references.

For example, searching for “self-esteem NOT eating disorders” finds articles that mention self-esteem but removes any articles that mention eating disorders.

Citation searching is a method to find articles that have been cited by other publications.

Use citation searching (or cited reference searching) to:

You can use cited reference searching in:

Cited reference searching can complement your literature search. However be careful not to just look at papers that have been cited in isolation. A robust literature search is also needed to limit publication bias.

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Literature Review: Developing a search strategy

From research question to search strategy

Keeping a record of your search activity

Good search practice could involve keeping a search diary or document detailing your search activities (Phelps et. al. 2007, pp. 128-149), so that you can keep track of effective search terms, or to help others to reproduce your steps and get the same results. 

This record could be a document, table or spreadsheet with:

A search planner may help you to organise you thoughts prior to conducting your search. If you have any problems with organising your thoughts prior, during and after searching please contact your Library  Faculty Team   for individual help.

Literature search cycle

search strategy for research paper example

Have a search framework

Search frameworks are mnemonics which can help you focus your research question. They are also useful in helping you to identify the concepts and terms you will use in your literature search.

PICO is a search framework commonly used in the health sciences to focus clinical questions.  As an example, you work in an aged care facility and are interested in whether cranberry juice might help reduce the common occurrence of urinary tract infections.  The PICO framework would look like this:

Now that the issue has been broken up to its elements, it is easier to turn it into an answerable research question: “Does cranberry juice help reduce urinary tract infections in people living in aged care facilities?”

Other frameworks may be helpful, depending on your question and your field of interest. PICO can be adapted to PICOT (which adds T ime) or PICOS (which adds S tudy design), or PICOC (adding C ontext).

For qualitative questions you could use

For questions about causes or risk,

For evaluations of interventions or policies, 

See the University of Notre Dame Australia’s examples of some of these frameworks. 

You can also try some PICO examples in the National Library of Medicine's PubMed training site: Using PICO to frame clinical questions.

Different search strategies

Contact Your Faculty Team Librarian

Faculty librarians are here to provide assistance to students, researchers and academic staff by providing expert searching advice, research and curriculum support.

Further reading

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How to write a search strategy for your systematic review

Home | Blog | How To | How to write a search strategy for your systematic review

Practical tips to write a search strategy for your systematic review

With a great review question and a clear set of eligibility criteria already mapped out, it’s now time to plan the search strategy. The medical literature is vast. Your team plans a thorough and methodical search, but you also know that resources and interest in the project are finite. At this stage it might feel like you have a mountain to climb.

The bottom line? You will have to sift through some irrelevant search results to find the studies that you need for your review. Capturing a proportion of irrelevant records in your search is necessary to ensure that it identifies as many relevant records as possible. This is the trade-off of precision versus sensitivity and, because systematic reviews aim to be as comprehensive as possible, it is best to favour sensitivity – more is more.

By now, the size of this task might be sounding alarm bells. The good news is that a range of techniques and web-based tools can help to make searching more efficient and save you time. We’ll look at some of them as we walk through the four main steps of searching for studies:

Searching is a specialist discipline and the information given here is not intended to replace the advice of a skilled professional. Before we look at each of the steps in turn, the most important systematic reviewer pro-tip for searching is:

 Pro Tip – Talk to your librarian and do it early!

1. decide where to search .

It’s important to come up with a comprehensive list of sources to search so that you don’t miss anything potentially relevant. In clinical medicine, your first stop will likely be the databases MEDLINE , Embase , and CENTRAL . Depending on the subject of the review, it might also be appropriate to run the search in databases that cover specific geographical regions or specialist areas, such as traditional Chinese medicine.

In addition to these databases, you’ll also search for grey literature (essentially, research that was not published in journals). That’s because your search of bibliographic databases will not find relevant information if it is part of, for example:

Over-reliance on published data introduces bias in favour of positive results. Studies with positive results are more likely to be submitted to journals, published in journals, and therefore indexed in databases. This is publication bias and systematic reviews seek to minimise its effects by searching for grey literature.

2. Write and refine the search 

Search terms are derived from key concepts in the review question and from the inclusion and exclusion criteria that are specified in the protocol or research plan.

Keywords will be searched for in the title or abstract of the records in the database. They are often truncated (for example, a search for therap* to find therapy, therapies, therapist). They might also use wildcards to allow for spelling variants and plurals (for example, wom#n to find woman and women). The symbols used to perform truncation and wildcard searches vary by database.

Index terms  

Using index terms such as MeSH and Emtree in a search can improve its performance. Indexers with subject area expertise work through databases and tag each record with subject terms from a prespecified controlled vocabulary.

This indexing can save review teams a lot of time that would otherwise be spent sifting through irrelevant records. Using index terms in your search, for example, can help you find the records that are actually about the topic of interest (tagged with the index term) but ignore those that contain only a brief mention of it (not tagged with the index term).

Indexers assign terms based on a careful read of each study, rather than whether or not the study contains certain words. So the index terms enable the retrieval of relevant records that cannot be captured by a simple search for the keyword or phrase.

Use a combination

Relying solely on index terms is not advisable. Doing so could miss a relevant record that for some reason (indexer’s judgment, time lag between a record being listed in a database and being indexed) has not been tagged with an index term that would enable you to retrieve it. Good search strategies include both index terms and keywords.

search strategy for research paper example

Let’s see how this works in a real review! Figure 2 shows the search strategy for the review ‘Wheat flour fortification with iron and other micronutrients for reducing anaemia and improving iron status in populations’. This strategy combines index terms and keywords using the Boolean operators AND, OR, and NOT. OR is used first to reach as many records as possible before AND and NOT are used to narrow them down.

search strategy for research paper example

Writing a search strategy is an iterative process. A good plan is  to try out a new strategy and check that it has picked up the key studies that you would expect it to find based on your existing knowledge of the topic area. If it hasn’t, you can explore the reasons for this, revise the strategy, check it for errors, and try it again!

3. Run and record the search

Because of the different ways that individual databases are structured and indexed, a separate search strategy is needed for each database. This adds complexity to the search process, and it is important to keep a careful record of each search strategy as you run it. Search strategies can often be saved in the databases themselves, but it is a good idea to keep an offline copy as a back-up; Covidence allows you to store your search strategies online in your review settings.

The reporting of the search will be included in the methods section of your review and should follow the PRISMA guidelines. You can download a flow diagram from PRISMA’s website to help you log the number of records retrieved from the search and the subsequent decisions about the inclusion or exclusion of studies. The PRISMA-S extension provides guidance on reporting literature searches.

search strategy for research paper example

It is very important that search strategies are reproduced in their entirety (preferably using copy and paste to avoid typos) as part of the published review so that they can be studied and replicated by other researchers. Search strategies are often made available as an appendix because they are long and might otherwise interrupt the flow of the text in the methods section.

4. Manage the search results 

Once the search is done and you have recorded the process in enough detail to write up a thorough description in the methods section, you will move on to screening the results. This is an exciting stage in any review because it’s the first glimpse of what the search strategies have found. A large volume of results may be daunting but your search is very likely to have captured some irrelevant studies because of its high sensitivity, as we have already seen. Fortunately, it will be possible to exclude many of these irrelevant studies at the screening stage on the basis of the title and abstract alone 😅.

Search results from multiple databases can be collated in a single spreadsheet for screening. To benefit from process efficiencies, time-saving and easy collaboration with your team, you can import search results into a specialist tool such as Covidence. A key benefit of Covidence is that you can track decisions made about the inclusion or exclusion of studies in a simple workflow and resolve conflicting decisions quickly and transparently. Covidence currently supports three formats for file imports of search results:

If you’d like to try this feature of Covidence but don’t have any data yet, you can download some ready-made sample data .

And you’re done!

There is a lot to think about when planning a search strategy. With practice, expert help, and the right tools your team can complete the search process with confidence.

This blog post is part of the Covidence series on how to write a systematic review.

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[1] Witt  KG, Hetrick  SE, Rajaram  G, Hazell  P, Taylor Salisbury  TL, Townsend  E, Hawton  K. Pharmacological interventions for self‐harm in adults . Cochrane Database of Systematic Reviews 2020, Issue 12. Art. No.: CD013669. DOI: 10.1002/14651858.CD013669.pub2. Accessed 02 February 2021

search strategy for research paper example

Laura Mellor. Portsmouth, UK

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How to Write a Research Paper

Instruction and Reference Librarian

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...to Lori Micho, Johnson & Wales University, for allowing us to use her Research Process LibGuide as a template.

Where to Begin

This guide will provide you with information on writing a research paper, which typically consists of five broad steps. 

1.  Select a Topic

Develop   |  Formulate Questions/Thesis   |  Identify Keywords   |  Find Background Info   |  Refine

2.  Find Information

Articles   |  Books   |  Dissertations  |  eBooks  |  Proceedings  | Statistics   |  Websites   |  Search Strategies

3.  Evaluate

Evaluate Sources   |  Primary / Secondary   |  Scholarly / General

4.  Use

Take Notes   |   Quote, Paraphrase, Summarize

5.  Legal/Ethical

Citing References   |  Copyright   |  Plagiarism

search strategy for research paper example

Form and Style Review Home Page

DNP Search Strategy Description Sample A

Search strategy description samples: dnp search strategy description sample a.

In the example below, notes follow some of the paragraphs. Highlighted sentences are for emphasis only (do not highlight sentences in your study).

From Section 2: Background and Context of a DNP Project Study (Development of a Scope of Practice)

The practice focused question I sought to answer in this project study was, What is the scope of practice of the nurse practitioner in MIAM in California? There is much evidence showing that MIAM is a relatively new field without a clearly defined scope of practice. It also shows the importance of having a clearly defined scope of practice (Goh, 2009).

I used a variety of data bases in researching and developing my project. These include EBSCOhost and CINAHL. The key words searched were nurse practitioner scope of practice, MIAM, botox, botulinum toxin, dermal filler, evidence-based aesthetic, scope of practice barriers, full implementation scope of practice, lasers skin, complications botulinum toxin, adverse botulinum toxin, aesthetic dermatology, nurse aesthetic autonomy, medspa, medical spa, injectables, and minimally invasive plastic. I identified three themes in conducting these searches and reviewing the literature: the status of MIAM as a relatively new field, lack of structured training and accreditation, and lack of a clearly defined scope of practice.

Note the third sentence in the previous paragraph. Inclusion of keywords used to search the databases is helpful to readers as well as other researchers.
Note the last sentence in the previous paragraph. The author nicely synthesizes key learning from the literature review.

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Presenting a search strategy

Have you done a structured search related to a literature review or other work? Do you need to present how you found the articles you selected? Are you thinking about how you can present articles that you have found alongside the search, for example via a reference list to another article? Here you can see what information should be included in a search strategy presentation, and some examples of what it might look like.

What should be included in a search strategy presentation?

How can you present your search strategy.

What should a search strategy presentation contain?

Example of text in the methods section

The searches were conducted during June 2018 in the databases CINAHL, Web of Science and PubMed.

The Mesh terms identified for the PubMed search were adapted to corresponding terms in CINAHL. Every individual search term was supplemented with relevant free text terms. When appropriate, the free text terms have been truncated in order to include alternative word endings.

The search result was limited to articles that were written in English as well as articles published during the last ten years. The full search strategy is included as an appendix.

The database searches were complemented with manual review of the reference lists of relevant articles, which resulted in a few additional articles included in the study.

Examples from different databases

In the tables below we present searches in three different databases. In all databases we have used the topic " Patients' experience of day surgery ".

Example from CINAHL

MH = Exact Subject Heading

Example from PubMed

Example from web of science.

Students studying in the library in Solna.

Guide for students: Structured literature reviews

A step-by-step guide aimed at Master's students undertaking a structured literature review as part of their Master's thesis. In this guide we will go through the different steps of a structured literature review and provide tips on how to make your search strategy more structured and extensive.

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Guidance in information searching

Are you looking for scientific articles or writing references and need advice? You can get help from our librarians. We offer both drop-in via Zoom and booked consultations.

Opening hours drop-in support in Zoom

Appendix 2: Example search strategy to identify studies from electronic databases  

The development of a search strategy is an iterative process: one attempt will rarely produce the final strategy. Strategies are usually built up from a series of test searches and discussions of the results of those searches among the review team.

The first step is to break down the review question to help guide the development of search terms, using a structure such as PICOS.

For example:

It is not necessary to include all of the PICOS concepts in the search strategy. It is preferable to search for those concepts that can be clearly defined and translated into search terms. Concepts that are poorly defined, not likely to be included in journal abstracts, or not indexed in a consistent way, will be difficult to identify from database searches. If this is the case, using a broader search and then sifting through the identified studies may be preferable. This may apply particularly to the outcome(s) of studies as these are frequently not referred to in either the title or abstract of a database record.

Search filters are tested and in some cases validated strategies that can be used in a named database to identify specific types of study. They usually consist of a series of database index terms relating to study type combined with free text terms describing the methods used in conducting that type of research. There are filters available that will, for example, reliably identify RCTs in MEDLINE and in EMBASE, but filters for use in other databases or to identify other study types are limited. The development and validation of filters to identify other study types, such as diagnostic accuracy studies and qualitative research, is ongoing. = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >1 , = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >2 , = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >3 , = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >4 A useful source of information about search filters is the website maintained by the InterTASC Information Specialists’ Subgroup www.york.ac.uk/inst/crd/intertasc/ which lists both published search filters and research on their development and use.

Once the concepts of the search have been determined, the next stage is to produce a list of synonyms, abbreviations and spelling variants which may be used by authors. Similar research is often described using very different terms. To reflect this variation, a search strategy will usually comprise both indexing terms (if the database has a thesaurus or controlled vocabulary) and ‘free text’ terms and synonyms (from the database record’s title and abstract) to ensure that as many relevant papers are retrieved as possible. For example, when searching MEDLINE for studies about myocardial infarction, the free text term “heart attack” should be used as well as the Medical Subject Heading (MeSH) term “Myocardial Infarction”. Identifying appropriate indexing terms can be done by searching for key papers and checking how they have been indexed, consulting clinical experts in the review team and advisory group, as well as by scanning the thesaurus for relevant terms.

When selecting free text terms to use in the strategy it is important to take account of alternative spellings (including US and British English variants), abbreviations, synonyms, geographical variation, and changes in terminology over time. Sometimes it can also be useful to search for common mis-spellings, for example “asprin” when you want to retrieve studies of aspirin.

The important thing is to compile imaginatively and to check the indexing terms used in known relevant publications. Once a list of potential search terms has been compiled for each of the concepts, the next stage is to identify relevant subject headings which have been used to describe the topic in the databases you plan to search. For example with post-operative infection the following Medical Subject Headings (MeSH) are available for use in MEDLINE:

Bacterial Infections

Postoperative Complications

Surgical Wound Infection

Prosthesis-Related Infections

Infection Control

Some of these terms are "high level" that encompass narrower or more specific terms. To capture these narrower terms, in those databases that offer the facility, it is possible to ‘explode’ the high level term and so search for many terms at once. The explosion facility within a database makes use of the hierarchical thesaurus. Using the command “exp Bacterial Infections/ ” in the OvidSP interface to MEDLINE will retrieve papers indexed with that term but will also automatically retrieve papers indexed with the narrower terms Bacteremia, Hemorrhagic Septicemia, Central Nervous System Bacterial Infections, etc. as displayed in the section of the MeSH below.

Bacterial Infections/

Hemorrhagic Septicemia

Central Nervous System Bacterial Infections

Endocarditis, Bacterial

Eye Infections, Bacterial

Fournier Gangrene

The subject headings should be added to the concept list relating to the post-operative infection concept so that a first test search strategy for MEDLINE includes a mixture of text terms and MeSH headings.

bacterial adj infect$.ti,ab.                                

(postoperative adj complication$ or post adj operative adj complication$).ti,ab.

surgical adj wound adj infection$.ti,ab.

prosthesis-related adj infection$.ti,ab.

hip adj replacement adj3 infection$.ti,ab.



infection adj control.ti,ab.

bacterial adj contamination.ti,ab.

exp Bacterial Infections/

exp Postoperative Complications/

Surgical Wound Infection/

Prosthesis-Related Infections/

exp Infection Control/

The search has been written for the OvidSP search interface to MEDLINE and has commands specific to that interface:

adj      Words have to appear next to each other. Also retrieves hyphenated words.

adj3    Words have to appear within 3 words of each other. Other numbers can be used as required.

$        Truncation symbol, for example ‘complication$’ retrieves 'complications' as well as 'complication'.

.ti,ab   Restricts the search to title and abstract fields, to avoid retrieving unexpected results from the subject headings.

EXP     Explode the subject heading, to retrieve more specific terms

/         MeSH heading.

?        O ptional wild card character used within, or at the end of, a search term to substitute for one or no characters. Useful for retrieving documents with British and American word variants.

Each database interface has its own unique set of commands and, information about these will be on the database help pages.

Once a series of concepts that reflect the PICOS elements have been compiled they are then combined using Boolean logic (AND, OR, NOT) to create a set of results which should contain articles relating to the topic in question. The AND operator is used to ensure that all the search terms must appear in the record, for example searching for “prostate AND cancer” retrieves all records which contain both the term prostate and the term cancer. AND is used to narrow down or focus a search.

OR is used to accumulate similar search terms and thus makes searches larger. Searching for “heparin OR warfarin” retrieves all records where either heparin or warfarin or both are found. It is best to use the OR operator to combine terms relating to the same concept (e.g. all the postoperative infection terms in the example above) before narrowing down a search using the AND operator with another set of terms.

NOT is used to exclude records from a search. For example, “acupuncture NOT asthma” will retrieve all records which contain the term acupuncture, but not those which also contain the word asthma. NOT should be used with great care because it may have a larger effect than anticipated; a record may well discuss both the concept of interest and the one to be excluded.

The combination of concepts using the Boolean operators might develop as follows (for MEDLINE using the OVIDSP interface):

1       Hip Joint/

2       Hip Prosthesis/

3       Acetabulum/

4       hip replacement$.ti,ab.

5       total-hip replacement$.ti,ab.

6       total joint replacement$.ti,ab.

7       hip surgery.ti,ab.

8       hip operation$.ti,ab.

9       (hip adj3 prosthe$).ti,ab.

10     (hip adj3 arthroplasty).ti,ab.

11     1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9 or 10

12     exp Bacterial Infections/

13     exp Postoperative Complications/

14     Surgical Wound Infection/

14     Prosthesis-Related Infections/

16     Sepsis/

17     exp Anti-Infective Agents/

18     exp Infection Control/

19     exp Antibiotics/

20     Antibiotic Prophylaxis/

21       ((bacteri$ or wound$) adj2 (infect$ or contamin$)).ti,ab.

22       sepsis.ti,ab.

23       antibiotic$.ti,ab.

24       antimicrobial$.ti,ab.

25       anti-microbial$.ti,ab.

26       (anti$ adj infect$).ti,ab.

27       ultraclean.ti,ab.

28       hypersterile.ti,ab.

29       or/12-28

30       11 and 29

Sets 1 to 10 capture the concepts of hip replacement or hip surgery and are combined using OR to produce result set 11. Sets 12 to 28 capture the concepts of infection and infection prevention and are combined using OR to produce result set 29. The two sets of concepts are then combined to find the records which contain both concepts using AND to produce set 30.

The draft strategy can be tested on one database and the results checked by whether it retrieves papers that are already known to the team but were not used to develop the draft strategy. In addition, a small sample of the results of the test or scoping search can be examined by the review team to identify additional search terms (text words and indexing) or highlight potential limitations. The sample records need to be representative so bear in mind that the search results as output from the database will be listed in either alphabetical order by authors name, or by publication date or by date added to the database. Depending upon the complexity of the review topic, and consequently the search to be undertaken, this process may need to be repeated several times until an agreed strategy is formulated. If at all possible, the final search strategy should be peer reviewed to check for errors (spelling mistakes, incorrect use of operators, or failure to include relevant MeSH) that could reduce the recall of papers. = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >5  

At this point, the searches using other databases and resources can begin. However, this does not mean that search iterations should necessarily stop. If new search terms are identified during the review process they should be incorporated into the strategy or supplementary searches should be carried out.

Converting a final strategy for use in other databases requires care. While free text terms can usually be re-used in other databases you will need to identify one or possibly more matching relevant thesaurus terms used by the other databases. Each database thesaurus is unique so this procedure should be undertaken for each database being searched. For example, if you are searching MEDLINE for papers about “pressure sores” you would use the MeSH term “pressure ulcer” while if you were searching EMBASE you would need to use the EMTREE term “decubitus”.

If the search interface is also different you will need to make appropriate changes to the search operators used in the strategy. For example, some database providers use ‘$’ as the truncation symbol, while other database providers use ‘*’.

Not all databases include an abstract in the record and if this is the case you may want to make your search strategy more sensitive as you are relying solely upon terms being identified in the title (and any indexing fields). You can do this by using more synonyms and broader terms.

In some cases databases with web interfaces have a restricted range of search options and if this is the case searchers need to adopt pragmatic approaches and use very simple searches. For example, if there are limited options for combining terms using Boolean operators such as AND an alternative approach may be to run a number of separate searches on the database in place of one longer search.

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Literature Search Basics

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search strategy for research paper example

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Our Scientific Editors perform both substantive and copy editing of grant proposals, journal articles, and other reports of original research written by MD Anderson physicians and scientists for the professional literature, funding agencies, and other external (non-MD Anderson) audiences. 

Our librarians can provide expert searching for clinical or academic research, and hospital administration. This service is available to the faculty and staff at MD Anderson.


A literature search is a systematic search of all relevant literature on a specific topic. The literature search provides evidence to support many academic and clinical functions. The evidence gathered through a literature search can be used to answer a clinical question, write a research, review article or case report; prepare a presentation, write a grant application, and more.

Relevant literature can include journal articles, conference abstracts, books or book chapters, clinical trial registries and more.

Researchers, clinicians, and students search the literature all the time. So how is a literature search different?

As opposed to a background search where you are trying to review a topic, a literature search requires a methodical approach. To complete a literature search you will need:

This guide will walk you through the steps required to complete a literature search. 

search strategy for research paper example

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Trinity Search

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Writing a Literature Review

Getting your search right

Keyword searches, widening your search: truncation and wildcards, combining your terms: search operators, being more specific: phrase and proximity searching, subject headings, combining keyword and subject heading searches, using methodological search filters.

Test your strategy!

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Think about...

Your search is likely to be complex and involve multiple steps to do with different subjects, what are often called "strands" or "strings" in the search. Look at the appendices of existing reviews for an idea of what's involved in creating a comprehensive search.

Most people should start by finding all the articles on Topic A, then moving on to Topic B, then Topic C (and so on), then combining those strands together using AND (see Combining your terms: search operators below). This will then give you results that mention all those topics.

You will then need to adapt (or "translate") your strategy for each database depending on the searching options available on each one. A core of terms is used across multiple databases - this is the "systematic" part - BUT with additions and subtractions as necessary. While the words in the title and abstract might remain the same, it's highly likely the thesaurus terms (if they exist) will be different across the databases. You may need to leave out some strings completely; for example, let's say you are doing a study that needs to find Randomised Controlled Trials (RCTs) on a particular disease and its treatment. You will be looking in multiple databases for words to do with the condition, and also words that are used for RCTs. But when you are looking in databases that are composed entirely of RCTs (trials registers), the part of a search looking for RCTs doesn’t need to be included as it's redundant.

The techniques described below will help ensure you cover everything. Contact your Subject Librarian if you would like guidance on constructing your search.

This video from the University of Reading gives a good overview of literature searching tips and tricks:

Jump to 01:45 for truncation and 05:46 for wildcards.

Most searches have two elements - the "keywords" part and the "subject headings" part - for each topic. When you are initially constructing your search and trialling it in a database, you are likely to just add your keywords, click Search, and see how many that retrieves. But after that, for any type of comprehensive search, you should look at limiting your keywords to looking in specific search fields .

A field in this context is where the database only looks at one aspect of the information about the article. Common examples are the Author, Title, Abstract, and Journal Name. More esoteric ones could be fields like the CAS Registry Entry or Corporate Author.

In complex reviews like systematic, scoping and rapid reviews, the accepted wisdom is to limit these "keyword" searches to the Title and Abstract fields, plus (if available, and the search is looking to be comprehensive) any available "Author Keyword" or "Contributed Indexing" fields. It is vital that the keywords you use in these fields are identical - you are using the same words in the Title, Abstract and any related fields - and that you combine them using OR (see Combining your terms: search operators below)

A title, abstract and keyword search in MEDLINE

Using keyword searching limited to the Title/Abstract/Keywords fields should reduce the number of results which are retrieved in error or are only on the periphery of your subject. If you do this, please be aware that you will need to ensure that you have definitely also included all relevant subject headings in your search strategy (in databases that use controlled vocabulary) otherwise you risk missing out on useful results. It *is* quite possible that there will be no relevant subject headings in a particular search.

Although some databases will automatically search for variant spellings, mostly they will just search for the exact letters you type in. Use wildcard and truncation symbols to take control of your search and include variations to widen your search and ensure you don't miss something relevant.

A truncation symbol (*) retrieves any number of letters  - useful to find different word endings based on the root of a word: africa*  will find africa, african, africans, africaans agricultur*  will find agriculture, agricultural, agriculturalist

A wildcard symbol (?) replaces a single letter . It's useful for retrieving alternate spelling spellings (i.e. British vs American English) and simple plurals: wom?n  will find woman or women behavio?r  will find behaviour or behavior

Hint: Not all databases use the * and ? symbols - some may use different ones (! instead of *, for example), or not have the feature at all, so check the online help section of the database before you start.

Search operators (also called Boolean operators) allow you to include multiple words and concepts in your searches. This means you can search for all of your terms at once rather than carrying out multiple searches for each concept.

There are three main operators:

women OR female

search strategy for research paper example

Using OR will bring you back records containing either of your search terms. It will return items that include both terms, but will also return items that contain only one of the terms.

This will give you a broader range of results.

OR can be used to link together synonyms. These are then placed in brackets to show that they are all the same concept.

women AND Africa

Using AND will find items that contain both of your search terms, giving you a more specific set of results.

If you're getting too many results, using AND can be a good way to narrow your search.

women NOT Africa

Using NOT will find articles containing a particular term, but will exclude articles containing your second term.

Use this with caution - by excluding results you might miss out on key resources.

Sometimes your search may contain common words (i.e. development, communication) which will retrieve too many irrelevant records, even when using an AND search. On many databases, including Google, to look for a specific phrase, use inverted commas:

Your search will only bring back items containing these exact phrases.

Some databases automatically perform a phrase search if you do not use any search operators. For example, "agriculture africa" is not a phrase used in English so you may not find any items on the subject. Use AND in between your search words to avoid this.

On Scopus to search for an exact phrase use { } e.g. {agricultural development}. Using quotes on Scopus will find your words in the same field (e.g., title) but not necessarily next to one another. In this database, you need to be very careful with those brackets - {heart-attack} and {heart attack} will return different results because the dash is included. Wildcards are searched as actual characters, e.g. {health care?} returns results such as: Who pays for health care?

Some databases use proximity operators, which are a more advanced search function. You can use these to tell the database how close one word must be to another and, in some cases, in what order. This makes a search more specific and excludes irrelevant records.

For instance, if you were searching for references about women in Africa, you might retrieve irrelevant records for items about women published in Africa. Performing a proximity search will only retrieve the two words in the same sentence, making your search more accurate.

Each database has its own way of proximity searching, often with multiple ways of doing it, so it's important to check the online help before you start . Here are some examples of the variety of possible searches:

After completing your keywords search on a topic, you can move on to looking for appropriate subject headings.

Most databases have this controlled vocabulary feature (standardised subject headings or thesaurus terms - a bit like standard tags) which can help ensure you capture all the relevant studies; for example, MEDLINE, CENTRAL and PubMed use the exact same headings, which are called MeSH (Medical Subject Headings). Some of these headings will be the same in other related databases like CINAHL, but many of them will be slightly different, could be the same but have subtly different meanings, or not be there at all.

Not all databases have these types of subject headings - Web of Science and JSTOR don't allow you to search for subject headings like these, although you can of course search for subjects in them.

The easiest way to search for a subject heading is to go to the relevant area in the database that searches specifically for them; this might be called something like Thesaurus, Subject Headings, or similar. Then search for some of the words to do with your topic - not all of them at once, just a word on its own or a very simple phrase. Does this bring anything up? When you read the description, are you talking about the same thing?

You can then tell it to search for everything listed under that subject heading, then move on to looking for another subject heading. It's quite common for one topic to have several relevant headings.

Once you have found all the relevant headings, and made the database run searches for them, you will then combine them together using OR.

After you have found all the title/abstract/keywords for Topic A, and then all the relevant subject headings, you then combine those together using OR. You may need to go into the Search History section of the database to do this, and work out whether you can tick boxes next to your various searches to combine them, or have to type out something like "#1 OR #2".

How to combine title/abstract/keyword searches with subject searches in Ebsco's MEDLINE

This gives you a "super search" with everything in the database on that topic. It's likely to be a lot!

It might be that adding them together gives no extra results than the amount in either the keywords or the subject headings on their own. This is unusual, but not impossible:

A combined title, abstract, keywords and subject heading search in MEDLINE

You now go back to the start and for Topic B do the same title/abstract/keywords searches, then the relevant subject headings searches, then combine them as above. Then Topic C, and so on. Again, each of these super searches may have very high numbers - possibly millions.

Finally, you then combine all these super searches together, but this time using AND; they need to mention all the topics. It's possible that there are no articles in that database that mention all those things - the more subjects you AND together, the less results you are likely to find. However, it's also possible to end up with zero as there is a mistake in your search, and in most cases having zero results won't allow you to write your paper or thesis. So contact us if you think you have too few or two many results, and we can advise.

Methodological search filters are search terms or strategies that identify a topic or aspect. They are predefined, tried and tested filters which can be applied to a search.

Study types: 'systematic reviews', 'Randomised Controlled Trials'

Age groups: 'children', 'elderly'

Language: 'English'

They are available to select via the results filters displayed alongside your results and are normally applied at the very end of your search . For instance, on PubMed after running your results it is possible to limit by 'Ages' which gives predefined groupings such as 'Infant: birth-23 months'. These limits and filters are not always the same across the databases, so do be careful .


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