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References in Research – Types, Examples and Writing Guide

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References in Research

Definition:

References in research are a list of sources that a researcher has consulted or cited while conducting their study. They are an essential component of any academic work, including research papers, theses, dissertations, and other scholarly publications.

Types of References

There are several types of references used in research, and the type of reference depends on the source of information being cited. The most common types of references include:

References to books typically include the author’s name, title of the book, publisher, publication date, and place of publication.

Example: Smith, J. (2018). The Art of Writing. Penguin Books.

Journal Articles

References to journal articles usually include the author’s name, title of the article, name of the journal, volume and issue number, page numbers, and publication date.

Example: Johnson, T. (2021). The Impact of Social Media on Mental Health. Journal of Psychology, 32(4), 87-94.

Web sources

References to web sources should include the author or organization responsible for the content, the title of the page, the URL, and the date accessed.

Example: World Health Organization. (2020). Coronavirus disease (COVID-19) advice for the public. Retrieved from https://www.who.int/emergencies/disease/novel-coronavirus-2019/advice-for-public

Conference Proceedings

References to conference proceedings should include the author’s name, title of the paper, name of the conference, location of the conference, date of the conference, and page numbers.

Example: Chen, S., & Li, J. (2019). The Future of AI in Education. Proceedings of the International Conference on Educational Technology, Beijing, China, July 15-17, pp. 67-78.

References to reports typically include the author or organization responsible for the report, title of the report, publication date, and publisher.

Example: United Nations. (2020). The Sustainable Development Goals Report. United Nations.

Formats of References

Some common Formates of References with their examples are as follows:

APA (American Psychological Association) Style

The APA (American Psychological Association) Style has specific guidelines for formatting references used in academic papers, articles, and books. Here are the different reference formats in APA style with examples:

Author, A. A. (Year of publication). Title of book. Publisher.

Example : Smith, J. K. (2005). The psychology of social interaction. Wiley-Blackwell.

Journal Article

Author, A. A., Author, B. B., & Author, C. C. (Year of publication). Title of article. Title of Journal, volume number(issue number), page numbers.

Example : Brown, L. M., Keating, J. G., & Jones, S. M. (2012). The role of social support in coping with stress among African American adolescents. Journal of Research on Adolescence, 22(1), 218-233.

Author, A. A. (Year of publication or last update). Title of page. Website name. URL.

Example : Centers for Disease Control and Prevention. (2020, December 11). COVID-19: How to protect yourself and others. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html

Magazine article

Author, A. A. (Year, Month Day of publication). Title of article. Title of Magazine, volume number(issue number), page numbers.

Example : Smith, M. (2019, March 11). The power of positive thinking. Psychology Today, 52(3), 60-65.

Newspaper article:

Author, A. A. (Year, Month Day of publication). Title of article. Title of Newspaper, page numbers.

Example: Johnson, B. (2021, February 15). New study shows benefits of exercise on mental health. The New York Times, A8.

Edited book

Editor, E. E. (Ed.). (Year of publication). Title of book. Publisher.

Example : Thompson, J. P. (Ed.). (2014). Social work in the 21st century. Sage Publications.

Chapter in an edited book:

Author, A. A. (Year of publication). Title of chapter. In E. E. Editor (Ed.), Title of book (pp. page numbers). Publisher.

Example : Johnson, K. S. (2018). The future of social work: Challenges and opportunities. In J. P. Thompson (Ed.), Social work in the 21st century (pp. 105-118). Sage Publications.

MLA (Modern Language Association) Style

The MLA (Modern Language Association) Style is a widely used style for writing academic papers and essays in the humanities. Here are the different reference formats in MLA style:

Author’s Last name, First name. Title of Book. Publisher, Publication year.

Example : Smith, John. The Psychology of Social Interaction. Wiley-Blackwell, 2005.

Journal article

Author’s Last name, First name. “Title of Article.” Title of Journal, volume number, issue number, Publication year, page numbers.

Example : Brown, Laura M., et al. “The Role of Social Support in Coping with Stress among African American Adolescents.” Journal of Research on Adolescence, vol. 22, no. 1, 2012, pp. 218-233.

Author’s Last name, First name. “Title of Webpage.” Website Name, Publication date, URL.

Example : Centers for Disease Control and Prevention. “COVID-19: How to Protect Yourself and Others.” CDC, 11 Dec. 2020, https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.

Author’s Last name, First name. “Title of Article.” Title of Magazine, Publication date, page numbers.

Example : Smith, Mary. “The Power of Positive Thinking.” Psychology Today, Mar. 2019, pp. 60-65.

Newspaper article

Author’s Last name, First name. “Title of Article.” Title of Newspaper, Publication date, page numbers.

Example : Johnson, Bob. “New Study Shows Benefits of Exercise on Mental Health.” The New York Times, 15 Feb. 2021, p. A8.

Editor’s Last name, First name, editor. Title of Book. Publisher, Publication year.

Example : Thompson, John P., editor. Social Work in the 21st Century. Sage Publications, 2014.

Chapter in an edited book

Author’s Last name, First name. “Title of Chapter.” Title of Book, edited by Editor’s First Name Last name, Publisher, Publication year, page numbers.

Example : Johnson, Karen S. “The Future of Social Work: Challenges and Opportunities.” Social Work in the 21st Century, edited by John P. Thompson, Sage Publications, 2014, pp. 105-118.

Chicago Manual of Style

The Chicago Manual of Style is a widely used style for writing academic papers, dissertations, and books in the humanities and social sciences. Here are the different reference formats in Chicago style:

Example : Smith, John K. The Psychology of Social Interaction. Wiley-Blackwell, 2005.

Author’s Last name, First name. “Title of Article.” Title of Journal volume number, no. issue number (Publication year): page numbers.

Example : Brown, Laura M., John G. Keating, and Sarah M. Jones. “The Role of Social Support in Coping with Stress among African American Adolescents.” Journal of Research on Adolescence 22, no. 1 (2012): 218-233.

Author’s Last name, First name. “Title of Webpage.” Website Name. Publication date. URL.

Example : Centers for Disease Control and Prevention. “COVID-19: How to Protect Yourself and Others.” CDC. December 11, 2020. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.

Author’s Last name, First name. “Title of Article.” Title of Magazine, Publication date.

Example : Smith, Mary. “The Power of Positive Thinking.” Psychology Today, March 2019.

Author’s Last name, First name. “Title of Article.” Title of Newspaper, Publication date.

Example : Johnson, Bob. “New Study Shows Benefits of Exercise on Mental Health.” The New York Times, February 15, 2021.

Example : Thompson, John P., ed. Social Work in the 21st Century. Sage Publications, 2014.

Author’s Last name, First name. “Title of Chapter.” In Title of Book, edited by Editor’s First Name Last Name, page numbers. Publisher, Publication year.

Example : Johnson, Karen S. “The Future of Social Work: Challenges and Opportunities.” In Social Work in the 21st Century, edited by John P. Thompson, 105-118. Sage Publications, 2014.

Harvard Style

The Harvard Style, also known as the Author-Date System, is a widely used style for writing academic papers and essays in the social sciences. Here are the different reference formats in Harvard Style:

Author’s Last name, First name. Year of publication. Title of Book. Place of publication: Publisher.

Example : Smith, John. 2005. The Psychology of Social Interaction. Oxford: Wiley-Blackwell.

Author’s Last name, First name. Year of publication. “Title of Article.” Title of Journal volume number (issue number): page numbers.

Example: Brown, Laura M., John G. Keating, and Sarah M. Jones. 2012. “The Role of Social Support in Coping with Stress among African American Adolescents.” Journal of Research on Adolescence 22 (1): 218-233.

Author’s Last name, First name. Year of publication. “Title of Webpage.” Website Name. URL. Accessed date.

Example : Centers for Disease Control and Prevention. 2020. “COVID-19: How to Protect Yourself and Others.” CDC. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html. Accessed April 1, 2023.

Author’s Last name, First name. Year of publication. “Title of Article.” Title of Magazine, month and date of publication.

Example : Smith, Mary. 2019. “The Power of Positive Thinking.” Psychology Today, March 2019.

Author’s Last name, First name. Year of publication. “Title of Article.” Title of Newspaper, month and date of publication.

Example : Johnson, Bob. 2021. “New Study Shows Benefits of Exercise on Mental Health.” The New York Times, February 15, 2021.

Editor’s Last name, First name, ed. Year of publication. Title of Book. Place of publication: Publisher.

Example : Thompson, John P., ed. 2014. Social Work in the 21st Century. Thousand Oaks, CA: Sage Publications.

Author’s Last name, First name. Year of publication. “Title of Chapter.” In Title of Book, edited by Editor’s First Name Last Name, page numbers. Place of publication: Publisher.

Example : Johnson, Karen S. 2014. “The Future of Social Work: Challenges and Opportunities.” In Social Work in the 21st Century, edited by John P. Thompson, 105-118. Thousand Oaks, CA: Sage Publications.

Vancouver Style

The Vancouver Style, also known as the Uniform Requirements for Manuscripts Submitted to Biomedical Journals, is a widely used style for writing academic papers in the biomedical sciences. Here are the different reference formats in Vancouver Style:

Author’s Last name, First name. Title of Book. Edition number. Place of publication: Publisher; Year of publication.

Example : Smith, John K. The Psychology of Social Interaction. 2nd ed. Oxford: Wiley-Blackwell; 2005.

Author’s Last name, First name. Title of Article. Abbreviated Journal Title. Year of publication; volume number(issue number):page numbers.

Example : Brown LM, Keating JG, Jones SM. The Role of Social Support in Coping with Stress among African American Adolescents. J Res Adolesc. 2012;22(1):218-233.

Author’s Last name, First name. Title of Webpage. Website Name [Internet]. Publication date. [cited date]. Available from: URL.

Example : Centers for Disease Control and Prevention. COVID-19: How to Protect Yourself and Others [Internet]. 2020 Dec 11. [cited 2023 Apr 1]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.

Author’s Last name, First name. Title of Article. Title of Magazine. Year of publication; month and day of publication:page numbers.

Example : Smith M. The Power of Positive Thinking. Psychology Today. 2019 Mar 1:32-35.

Author’s Last name, First name. Title of Article. Title of Newspaper. Year of publication; month and day of publication:page numbers.

Example : Johnson B. New Study Shows Benefits of Exercise on Mental Health. The New York Times. 2021 Feb 15:A4.

Editor’s Last name, First name, editor. Title of Book. Edition number. Place of publication: Publisher; Year of publication.

Example: Thompson JP, editor. Social Work in the 21st Century. 1st ed. Thousand Oaks, CA: Sage Publications; 2014.

Author’s Last name, First name. Title of Chapter. In: Editor’s Last name, First name, editor. Title of Book. Edition number. Place of publication: Publisher; Year of publication. page numbers.

Example : Johnson KS. The Future of Social Work: Challenges and Opportunities. In: Thompson JP, editor. Social Work in the 21st Century. 1st ed. Thousand Oaks, CA: Sage Publications; 2014. p. 105-118.

Turabian Style

Turabian style is a variation of the Chicago style used in academic writing, particularly in the fields of history and humanities. Here are the different reference formats in Turabian style:

Author’s Last name, First name. Title of Book. Place of publication: Publisher, Year of publication.

Example : Smith, John K. The Psychology of Social Interaction. Oxford: Wiley-Blackwell, 2005.

Author’s Last name, First name. “Title of Article.” Title of Journal volume number, no. issue number (Year of publication): page numbers.

Example : Brown, LM, Keating, JG, Jones, SM. “The Role of Social Support in Coping with Stress among African American Adolescents.” J Res Adolesc 22, no. 1 (2012): 218-233.

Author’s Last name, First name. “Title of Webpage.” Name of Website. Publication date. Accessed date. URL.

Example : Centers for Disease Control and Prevention. “COVID-19: How to Protect Yourself and Others.” CDC. December 11, 2020. Accessed April 1, 2023. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.

Author’s Last name, First name. “Title of Article.” Title of Magazine, Month Day, Year of publication, page numbers.

Example : Smith, M. “The Power of Positive Thinking.” Psychology Today, March 1, 2019, 32-35.

Author’s Last name, First name. “Title of Article.” Title of Newspaper, Month Day, Year of publication.

Example : Johnson, B. “New Study Shows Benefits of Exercise on Mental Health.” The New York Times, February 15, 2021.

Editor’s Last name, First name, ed. Title of Book. Place of publication: Publisher, Year of publication.

Example : Thompson, JP, ed. Social Work in the 21st Century. Thousand Oaks, CA: Sage Publications, 2014.

Author’s Last name, First name. “Title of Chapter.” In Title of Book, edited by Editor’s Last name, First name, page numbers. Place of publication: Publisher, Year of publication.

Example : Johnson, KS. “The Future of Social Work: Challenges and Opportunities.” In Social Work in the 21st Century, edited by Thompson, JP, 105-118. Thousand Oaks, CA: Sage Publications, 2014.

IEEE (Institute of Electrical and Electronics Engineers) Style

IEEE (Institute of Electrical and Electronics Engineers) style is commonly used in engineering, computer science, and other technical fields. Here are the different reference formats in IEEE style:

Author’s Last name, First name. Book Title. Place of Publication: Publisher, Year of publication.

Example : Oppenheim, A. V., & Schafer, R. W. Discrete-Time Signal Processing. Upper Saddle River, NJ: Prentice Hall, 2010.

Author’s Last name, First name. “Title of Article.” Abbreviated Journal Title, vol. number, no. issue number, pp. page numbers, Month year of publication.

Example: Shannon, C. E. “A Mathematical Theory of Communication.” Bell System Technical Journal, vol. 27, no. 3, pp. 379-423, July 1948.

Conference paper

Author’s Last name, First name. “Title of Paper.” In Title of Conference Proceedings, Place of Conference, Date of Conference, pp. page numbers, Year of publication.

Example: Gupta, S., & Kumar, P. “An Improved System of Linear Discriminant Analysis for Face Recognition.” In Proceedings of the 2011 International Conference on Computer Science and Network Technology, Harbin, China, Dec. 2011, pp. 144-147.

Author’s Last name, First name. “Title of Webpage.” Name of Website. Date of publication or last update. Accessed date. URL.

Example : National Aeronautics and Space Administration. “Apollo 11.” NASA. July 20, 1969. Accessed April 1, 2023. https://www.nasa.gov/mission_pages/apollo/apollo11.html.

Technical report

Author’s Last name, First name. “Title of Report.” Name of Institution or Organization, Report number, Year of publication.

Example : Smith, J. R. “Development of a New Solar Panel Technology.” National Renewable Energy Laboratory, NREL/TP-6A20-51645, 2011.

Author’s Last name, First name. “Title of Patent.” Patent number, Issue date.

Example : Suzuki, H. “Method of Producing Carbon Nanotubes.” US Patent 7,151,019, December 19, 2006.

Standard Title. Standard number, Publication date.

Example : IEEE Standard for Floating-Point Arithmetic. IEEE Std 754-2008, August 29, 2008

ACS (American Chemical Society) Style

ACS (American Chemical Society) style is commonly used in chemistry and related fields. Here are the different reference formats in ACS style:

Author’s Last name, First name; Author’s Last name, First name. Title of Article. Abbreviated Journal Title Year, Volume, Page Numbers.

Example : Wang, Y.; Zhao, X.; Cui, Y.; Ma, Y. Facile Preparation of Fe3O4/graphene Composites Using a Hydrothermal Method for High-Performance Lithium Ion Batteries. ACS Appl. Mater. Interfaces 2012, 4, 2715-2721.

Author’s Last name, First name. Book Title; Publisher: Place of Publication, Year of Publication.

Example : Carey, F. A. Organic Chemistry; McGraw-Hill: New York, 2008.

Author’s Last name, First name. Chapter Title. In Book Title; Editor’s Last name, First name, Ed.; Publisher: Place of Publication, Year of Publication; Volume number, Chapter number, Page Numbers.

Example : Grossman, R. B. Analytical Chemistry of Aerosols. In Aerosol Measurement: Principles, Techniques, and Applications; Baron, P. A.; Willeke, K., Eds.; Wiley-Interscience: New York, 2001; Chapter 10, pp 395-424.

Author’s Last name, First name. Title of Webpage. Website Name, URL (accessed date).

Example : National Institute of Standards and Technology. Atomic Spectra Database. https://www.nist.gov/pml/atomic-spectra-database (accessed April 1, 2023).

Author’s Last name, First name. Patent Number. Patent Date.

Example : Liu, Y.; Huang, H.; Chen, H.; Zhang, W. US Patent 9,999,999, December 31, 2022.

Author’s Last name, First name; Author’s Last name, First name. Title of Article. In Title of Conference Proceedings, Publisher: Place of Publication, Year of Publication; Volume Number, Page Numbers.

Example : Jia, H.; Xu, S.; Wu, Y.; Wu, Z.; Tang, Y.; Huang, X. Fast Adsorption of Organic Pollutants by Graphene Oxide. In Proceedings of the 15th International Conference on Environmental Science and Technology, American Chemical Society: Washington, DC, 2017; Volume 1, pp 223-228.

AMA (American Medical Association) Style

AMA (American Medical Association) style is commonly used in medical and scientific fields. Here are the different reference formats in AMA style:

Author’s Last name, First name. Article Title. Journal Abbreviation. Year; Volume(Issue):Page Numbers.

Example : Jones, R. A.; Smith, B. C. The Role of Vitamin D in Maintaining Bone Health. JAMA. 2019;321(17):1765-1773.

Author’s Last name, First name. Book Title. Edition number. Place of Publication: Publisher; Year.

Example : Guyton, A. C.; Hall, J. E. Textbook of Medical Physiology. 13th ed. Philadelphia, PA: Saunders; 2015.

Author’s Last name, First name. Chapter Title. In: Editor’s Last name, First name, ed. Book Title. Edition number. Place of Publication: Publisher; Year: Page Numbers.

Example: Rajakumar, K. Vitamin D and Bone Health. In: Holick, M. F., ed. Vitamin D: Physiology, Molecular Biology, and Clinical Applications. 2nd ed. New York, NY: Springer; 2010:211-222.

Author’s Last name, First name. Webpage Title. Website Name. URL. Published date. Updated date. Accessed date.

Example : National Cancer Institute. Breast Cancer Prevention (PDQ®)–Patient Version. National Cancer Institute. https://www.cancer.gov/types/breast/patient/breast-prevention-pdq. Published October 11, 2022. Accessed April 1, 2023.

Author’s Last name, First name. Conference presentation title. In: Conference Title; Conference Date; Place of Conference.

Example : Smith, J. R. Vitamin D and Bone Health: A Meta-Analysis. In: Proceedings of the Annual Meeting of the American Society for Bone and Mineral Research; September 20-23, 2022; San Diego, CA.

Thesis or dissertation

Author’s Last name, First name. Title of Thesis or Dissertation. Degree level [Doctoral dissertation or Master’s thesis]. University Name; Year.

Example : Wilson, S. A. The Effects of Vitamin D Supplementation on Bone Health in Postmenopausal Women [Doctoral dissertation]. University of California, Los Angeles; 2018.

ASCE (American Society of Civil Engineers) Style

The ASCE (American Society of Civil Engineers) style is commonly used in civil engineering fields. Here are the different reference formats in ASCE style:

Author’s Last name, First name. “Article Title.” Journal Title, volume number, issue number (year): page numbers. DOI or URL (if available).

Example : Smith, J. R. “Evaluation of the Effectiveness of Sustainable Drainage Systems in Urban Areas.” Journal of Environmental Engineering, vol. 146, no. 3 (2020): 04020010. https://doi.org/10.1061/(ASCE)EE.1943-7870.0001668.

Example : McCuen, R. H. Hydrologic Analysis and Design. 4th ed. Upper Saddle River, NJ: Pearson Education; 2013.

Author’s Last name, First name. “Chapter Title.” In: Editor’s Last name, First name, ed. Book Title. Edition number. Place of Publication: Publisher; Year: page numbers.

Example : Maidment, D. R. “Floodplain Management in the United States.” In: Shroder, J. F., ed. Treatise on Geomorphology. San Diego, CA: Academic Press; 2013: 447-460.

Author’s Last name, First name. “Paper Title.” In: Conference Title; Conference Date; Location. Place of Publication: Publisher; Year: page numbers.

Example: Smith, J. R. “Sustainable Drainage Systems for Urban Areas.” In: Proceedings of the ASCE International Conference on Sustainable Infrastructure; November 6-9, 2019; Los Angeles, CA. Reston, VA: American Society of Civil Engineers; 2019: 156-163.

Author’s Last name, First name. “Report Title.” Report number. Place of Publication: Publisher; Year.

Example : U.S. Army Corps of Engineers. “Hurricane Sandy Coastal Risk Reduction Program, New York and New Jersey.” Report No. P-15-001. Washington, DC: U.S. Army Corps of Engineers; 2015.

CSE (Council of Science Editors) Style

The CSE (Council of Science Editors) style is commonly used in the scientific and medical fields. Here are the different reference formats in CSE style:

Author’s Last name, First Initial. Middle Initial. “Article Title.” Journal Title. Year;Volume(Issue):Page numbers.

Example : Smith, J.R. “Evaluation of the Effectiveness of Sustainable Drainage Systems in Urban Areas.” Journal of Environmental Engineering. 2020;146(3):04020010.

Author’s Last name, First Initial. Middle Initial. Book Title. Edition number. Place of Publication: Publisher; Year.

Author’s Last name, First Initial. Middle Initial. “Chapter Title.” In: Editor’s Last name, First Initial. Middle Initial., ed. Book Title. Edition number. Place of Publication: Publisher; Year:Page numbers.

Author’s Last name, First Initial. Middle Initial. “Paper Title.” In: Conference Title; Conference Date; Location. Place of Publication: Publisher; Year.

Example : Smith, J.R. “Sustainable Drainage Systems for Urban Areas.” In: Proceedings of the ASCE International Conference on Sustainable Infrastructure; November 6-9, 2019; Los Angeles, CA. Reston, VA: American Society of Civil Engineers; 2019.

Author’s Last name, First Initial. Middle Initial. “Report Title.” Report number. Place of Publication: Publisher; Year.

Bluebook Style

The Bluebook style is commonly used in the legal field for citing legal documents and sources. Here are the different reference formats in Bluebook style:

Case citation

Case name, volume source page (Court year).

Example : Brown v. Board of Education, 347 U.S. 483 (1954).

Statute citation

Name of Act, volume source § section number (year).

Example : Clean Air Act, 42 U.S.C. § 7401 (1963).

Regulation citation

Name of regulation, volume source § section number (year).

Example: Clean Air Act, 40 C.F.R. § 52.01 (2019).

Book citation

Author’s Last name, First Initial. Middle Initial. Book Title. Edition number (if applicable). Place of Publication: Publisher; Year.

Example: Smith, J.R. Legal Writing and Analysis. 3rd ed. New York, NY: Aspen Publishers; 2015.

Journal article citation

Author’s Last name, First Initial. Middle Initial. “Article Title.” Journal Title. Volume number (year): first page-last page.

Example: Garcia, C. “The Right to Counsel: An International Comparison.” International Journal of Legal Information. 43 (2015): 63-94.

Website citation

Author’s Last name, First Initial. Middle Initial. “Page Title.” Website Title. URL (accessed month day, year).

Example : United Nations. “Universal Declaration of Human Rights.” United Nations. https://www.un.org/en/universal-declaration-human-rights/ (accessed January 3, 2023).

Oxford Style

The Oxford style, also known as the Oxford referencing system or the documentary-note citation system, is commonly used in the humanities, including literature, history, and philosophy. Here are the different reference formats in Oxford style:

Author’s Last name, First name. Book Title. Place of Publication: Publisher, Year of Publication.

Example : Smith, John. The Art of Writing. New York: Penguin, 2020.

Author’s Last name, First name. “Article Title.” Journal Title volume, no. issue (year): page range.

Example: Garcia, Carlos. “The Role of Ethics in Philosophy.” Philosophy Today 67, no. 3 (2019): 53-68.

Chapter in an edited book citation

Author’s Last name, First name. “Chapter Title.” In Book Title, edited by Editor’s Name, page range. Place of Publication: Publisher, Year of Publication.

Example : Lee, Mary. “Feminism in the 21st Century.” In The Oxford Handbook of Feminism, edited by Jane Smith, 51-69. Oxford: Oxford University Press, 2018.

Author’s Last name, First name. “Page Title.” Website Title. URL (accessed day month year).

Example : Jones, David. “The Importance of Learning Languages.” Oxford Language Center. https://www.oxfordlanguagecenter.com/importance-of-learning-languages/ (accessed 3 January 2023).

Dissertation or thesis citation

Author’s Last name, First name. “Title of Dissertation/Thesis.” PhD diss., University Name, Year of Publication.

Example : Brown, Susan. “The Art of Storytelling in American Literature.” PhD diss., University of Oxford, 2020.

Newspaper article citation

Author’s Last name, First name. “Article Title.” Newspaper Title, Month Day, Year.

Example : Robinson, Andrew. “New Developments in Climate Change Research.” The Guardian, September 15, 2022.

AAA (American Anthropological Association) Style

The American Anthropological Association (AAA) style is commonly used in anthropology research papers and journals. Here are the different reference formats in AAA style:

Author’s Last name, First name. Year of Publication. Book Title. Place of Publication: Publisher.

Example : Smith, John. 2019. The Anthropology of Food. New York: Routledge.

Author’s Last name, First name. Year of Publication. “Article Title.” Journal Title volume, no. issue: page range.

Example : Garcia, Carlos. 2021. “The Role of Ethics in Anthropology.” American Anthropologist 123, no. 2: 237-251.

Author’s Last name, First name. Year of Publication. “Chapter Title.” In Book Title, edited by Editor’s Name, page range. Place of Publication: Publisher.

Example: Lee, Mary. 2018. “Feminism in Anthropology.” In The Oxford Handbook of Feminism, edited by Jane Smith, 51-69. Oxford: Oxford University Press.

Author’s Last name, First name. Year of Publication. “Page Title.” Website Title. URL (accessed day month year).

Example : Jones, David. 2020. “The Importance of Learning Languages.” Oxford Language Center. https://www.oxfordlanguagecenter.com/importance-of-learning-languages/ (accessed January 3, 2023).

Author’s Last name, First name. Year of Publication. “Title of Dissertation/Thesis.” PhD diss., University Name.

Example : Brown, Susan. 2022. “The Art of Storytelling in Anthropology.” PhD diss., University of California, Berkeley.

Author’s Last name, First name. Year of Publication. “Article Title.” Newspaper Title, Month Day.

Example : Robinson, Andrew. 2021. “New Developments in Anthropology Research.” The Guardian, September 15.

AIP (American Institute of Physics) Style

The American Institute of Physics (AIP) style is commonly used in physics research papers and journals. Here are the different reference formats in AIP style:

Example : Johnson, S. D. 2021. “Quantum Computing and Information.” Journal of Applied Physics 129, no. 4: 043102.

Example : Feynman, Richard. 2018. The Feynman Lectures on Physics. New York: Basic Books.

Example : Jones, David. 2020. “The Future of Quantum Computing.” In The Handbook of Physics, edited by John Smith, 125-136. Oxford: Oxford University Press.

Conference proceedings citation

Author’s Last name, First name. Year of Publication. “Title of Paper.” Proceedings of Conference Name, date and location: page range. Place of Publication: Publisher.

Example : Chen, Wei. 2019. “The Applications of Nanotechnology in Solar Cells.” Proceedings of the 8th International Conference on Nanotechnology, July 15-17, Tokyo, Japan: 224-229. New York: AIP Publishing.

Example : American Institute of Physics. 2022. “About AIP Publishing.” AIP Publishing. https://publishing.aip.org/about-aip-publishing/ (accessed January 3, 2023).

Patent citation

Author’s Last name, First name. Year of Publication. Patent Number.

Example : Smith, John. 2018. US Patent 9,873,644.

References Writing Guide

Here are some general guidelines for writing references:

• Follow the citation style guidelines: Different disciplines and journals may require different citation styles (e.g., APA, MLA, Chicago). It is important to follow the specific guidelines for the citation style required.
• Include all necessary information : Each citation should include enough information for readers to locate the source. For example, a journal article citation should include the author(s), title of the article, journal title, volume number, issue number, page numbers, and publication year.
• Use proper formatting: Citation styles typically have specific formatting requirements for different types of sources. Make sure to follow the proper formatting for each citation.
• Order citations alphabetically: If listing multiple sources, they should be listed alphabetically by the author’s last name.
• Be consistent: Use the same citation style throughout the entire paper or project.
• Check for accuracy: Double-check all citations to ensure accuracy, including correct spelling of author names and publication information.
• Use reputable sources: When selecting sources to cite, choose reputable and authoritative sources. Avoid sources that are biased or unreliable.
• Include all sources: Make sure to include all sources used in the research, including those that were not directly quoted but still informed the work.
• Use online tools : There are online tools available (e.g., citation generators) that can help with formatting and organizing references.

Purpose of References in Research

References in research serve several purposes:

• To give credit to the original authors or sources of information used in the research. It is important to acknowledge the work of others and avoid plagiarism.
• To provide evidence for the claims made in the research. References can support the arguments, hypotheses, or conclusions presented in the research by citing relevant studies, data, or theories.
• To allow readers to find and verify the sources used in the research. References provide the necessary information for readers to locate and access the sources cited in the research, which allows them to evaluate the quality and reliability of the information presented.
• To situate the research within the broader context of the field. References can show how the research builds on or contributes to the existing body of knowledge, and can help readers to identify gaps in the literature that the research seeks to address.

Importance of References in Research

References play an important role in research for several reasons:

• Credibility : By citing authoritative sources, references lend credibility to the research and its claims. They provide evidence that the research is based on a sound foundation of knowledge and has been carefully researched.
• Avoidance of Plagiarism : References help researchers avoid plagiarism by giving credit to the original authors or sources of information. This is important for ethical reasons and also to avoid legal repercussions.
• Reproducibility : References allow others to reproduce the research by providing detailed information on the sources used. This is important for verification of the research and for others to build on the work.
• Context : References provide context for the research by situating it within the broader body of knowledge in the field. They help researchers to understand where their work fits in and how it builds on or contributes to existing knowledge.
• Evaluation : References provide a means for others to evaluate the research by allowing them to assess the quality and reliability of the sources used.

Advantages of References in Research

There are several advantages of including references in research:

• Acknowledgment of Sources: Including references gives credit to the authors or sources of information used in the research. This is important to acknowledge the original work and avoid plagiarism.
• Evidence and Support : References can provide evidence to support the arguments, hypotheses, or conclusions presented in the research. This can add credibility and strength to the research.
• Reproducibility : References provide the necessary information for others to reproduce the research. This is important for the verification of the research and for others to build on the work.
• Context : References can help to situate the research within the broader body of knowledge in the field. This helps researchers to understand where their work fits in and how it builds on or contributes to existing knowledge.
• Evaluation : Including references allows others to evaluate the research by providing a means to assess the quality and reliability of the sources used.
• Ongoing Conversation: References allow researchers to engage in ongoing conversations and debates within their fields. They can show how the research builds on or contributes to the existing body of knowledge.

About the author

Muhammad Hassan

Researcher, Academic Writer, Web developer

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• Referencing

A Quick Guide to Harvard Referencing | Citation Examples

Published on 14 February 2020 by Jack Caulfield . Revised on 15 September 2023.

Referencing is an important part of academic writing. It tells your readers what sources you’ve used and how to find them.

Harvard is the most common referencing style used in UK universities. In Harvard style, the author and year are cited in-text, and full details of the source are given in a reference list .

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Table of contents

Harvard in-text citation, creating a harvard reference list, harvard referencing examples, referencing sources with no author or date, frequently asked questions about harvard referencing.

A Harvard in-text citation appears in brackets beside any quotation or paraphrase of a source. It gives the last name of the author(s) and the year of publication, as well as a page number or range locating the passage referenced, if applicable:

Note that ‘p.’ is used for a single page, ‘pp.’ for multiple pages (e.g. ‘pp. 1–5’).

An in-text citation usually appears immediately after the quotation or paraphrase in question. It may also appear at the end of the relevant sentence, as long as it’s clear what it refers to.

When your sentence already mentions the name of the author, it should not be repeated in the citation:

Sources with multiple authors

When you cite a source with up to three authors, cite all authors’ names. For four or more authors, list only the first name, followed by ‘ et al. ’:

Sources with no page numbers

Some sources, such as websites , often don’t have page numbers. If the source is a short text, you can simply leave out the page number. With longer sources, you can use an alternate locator such as a subheading or paragraph number if you need to specify where to find the quote:

Multiple citations at the same point

When you need multiple citations to appear at the same point in your text – for example, when you refer to several sources with one phrase – you can present them in the same set of brackets, separated by semicolons. List them in order of publication date:

Multiple sources with the same author and date

If you cite multiple sources by the same author which were published in the same year, it’s important to distinguish between them in your citations. To do this, insert an ‘a’ after the year in the first one you reference, a ‘b’ in the second, and so on:

Prevent plagiarism, run a free check.

A bibliography or reference list appears at the end of your text. It lists all your sources in alphabetical order by the author’s last name, giving complete information so that the reader can look them up if necessary.

The reference entry starts with the author’s last name followed by initial(s). Only the first word of the title is capitalised (as well as any proper nouns).

Sources with multiple authors in the reference list

As with in-text citations, up to three authors should be listed; when there are four or more, list only the first author followed by ‘ et al. ’:

Reference list entries vary according to source type, since different information is relevant for different sources. Formats and examples for the most commonly used source types are given below.

• Entire book
• Book chapter
• Translated book
• Edition of a book

Journal articles

• Print journal
• Online-only journal with DOI
• Online-only journal with no DOI
• General web page
• Online article or blog
• Social media post

Sometimes you won’t have all the information you need for a reference. This section covers what to do when a source lacks a publication date or named author.

No publication date

When a source doesn’t have a clear publication date – for example, a constantly updated reference source like Wikipedia or an obscure historical document which can’t be accurately dated – you can replace it with the words ‘no date’:

Note that when you do this with an online source, you should still include an access date, as in the example.

When a source lacks a clearly identified author, there’s often an appropriate corporate source – the organisation responsible for the source – whom you can credit as author instead, as in the Google and Wikipedia examples above.

When that’s not the case, you can just replace it with the title of the source in both the in-text citation and the reference list:

Harvard referencing uses an author–date system. Sources are cited by the author’s last name and the publication year in brackets. Each Harvard in-text citation corresponds to an entry in the alphabetised reference list at the end of the paper.

Vancouver referencing uses a numerical system. Sources are cited by a number in parentheses or superscript. Each number corresponds to a full reference at the end of the paper.

A Harvard in-text citation should appear in brackets every time you quote, paraphrase, or refer to information from a source.

The citation can appear immediately after the quotation or paraphrase, or at the end of the sentence. If you’re quoting, place the citation outside of the quotation marks but before any other punctuation like a comma or full stop.

In Harvard referencing, up to three author names are included in an in-text citation or reference list entry. When there are four or more authors, include only the first, followed by ‘ et al. ’

Though the terms are sometimes used interchangeably, there is a difference in meaning:

• A reference list only includes sources cited in the text – every entry corresponds to an in-text citation .
• A bibliography also includes other sources which were consulted during the research but not cited.

Cite this Scribbr article

If you want to cite this source, you can copy and paste the citation or click the ‘Cite this Scribbr article’ button to automatically add the citation to our free Reference Generator.

Caulfield, J. (2023, September 15). A Quick Guide to Harvard Referencing | Citation Examples. Scribbr. Retrieved 2 April 2024, from https://www.scribbr.co.uk/referencing/harvard-style/

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Table of Contents

Every scientific paper builds on previous research – even if it’s in a new field, related studies will have preceded and informed it. In peer-reviewed articles, authors must give credit to this previous research, through citations and references. Not only does this show clearly where the current research came from, but it also helps readers understand the content of the paper better.

There is no optimum number of references for an academic article but depending on the subject you could be dealing with more than 100 different papers, conference reports, video articles, medical guidelines or any number of other resources.

That’s a lot of content to manage. Before submitting your manuscript, this needs to be checked, cross-references in the text and the list, organized and formatted.

The exact content and format of the citations and references in your paper will depend on the journal you aim to publish in, so the first step is to check the journal’s Guide for Authors before you submit.

There are two main points to pay attention to – consistency and accuracy. When you go through your manuscript to edit or proofread it, look closely at the citations within the text. Are they all the same? For example, if the journal prefers the citations to be in the format (name, year), make sure they’re all the same: (Smith, 2016).

Your citations must also be accurate and complete. Do they match your references list? Each citation should be included in the list, so cross-checking is important. It’s also common for journals to prefer that most, if not all, of the articles listed in your references be cited within the text – after all, these should be studies that contributed to the knowledge underpinning your work, not just your bedtime reading. So go through them carefully, noting any missing references or citations and filling the gaps.

Each journal has its own requirements when it comes to the content and format of references, as well as where and how you should include them in your submission, so double-check before you hit send!

In general, a reference will include authors’ names and initials, the title of the article, name of the journal, volume and issue, date, page numbers and DOI. On ScienceDirect, articles are linked to their original source (if also published on ScienceDirect) or to their Scopus record, so including the DOI can help link to the correct article.

A spotless reference list

Luckily, compiling and editing the references in your scientific manuscript can be easy – and it no longer has to be manual. Management tools like Mendeley can keep track of all your references, letting you share them with your collaborators. With the Word plugin, it’s possible to select the right citation style for the journal you’re submitting to and the tool will format your references automatically.

Like with any other part of your manuscript, it’s important to make sure your reference list has been checked and edited. Elsevier Author Services Language Editing can help, with professional manuscript editing that will help make sure your references don’t hold you back from publication.

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Reference List: Common Reference List Examples

Article (with doi).

Alvarez, E., & Tippins, S. (2019). Socialization agents that Puerto Rican college students use to make financial decisions. Journal of Social Change , 11 (1), 75–85. https://doi.org/10.5590/JOSC.2019.11.1.07

Laplante, J. P., & Nolin, C. (2014). Consultas and socially responsible investing in Guatemala: A case study examining Maya perspectives on the Indigenous right to free, prior, and informed consent. Society & Natural Resources , 27 , 231–248. https://doi.org/10.1080/08941920.2013.861554

Use the DOI number for the source whenever one is available. DOI stands for "digital object identifier," a number specific to the article that can help others locate the source. In APA 7, format the DOI as a web address. Active hyperlinks for DOIs and URLs should be used for documents meant for screen reading. Present these hyperlinks in blue and underlined text (the default formatting in Microsoft Word), although plain black text is also acceptable. Be consistent in your formatting choice for DOIs and URLs throughout your reference list. Also see our Quick Answer FAQ, "Can I use the DOI format provided by library databases?"

Jerrentrup, A., Mueller, T., Glowalla, U., Herder, M., Henrichs, N., Neubauer, A., & Schaefer, J. R. (2018). Teaching medicine with the help of “Dr. House.” PLoS ONE , 13 (3), Article e0193972. https://doi.org/10.1371/journal.pone.0193972

For journal articles that are assigned article numbers rather than page ranges, include the article number in place of the page range.

For more on citing electronic resources, see  Electronic Sources References .

Article (Without DOI)

Found in a common academic research database or in print.

Casler , T. (2020). Improving the graduate nursing experience through support on a social media platform. MEDSURG Nursing , 29 (2), 83–87.

If an article does not have a DOI and you retrieved it from a common academic research database through the university library, there is no need to include any additional electronic retrieval information. The reference list entry looks like the entry for a print copy of the article. (This format differs from APA 6 guidelines that recommended including the URL of a journal's homepage when the DOI was not available.) Note that APA 7 has additional guidance on reference list entries for articles found only in specific databases or archives such as Cochrane Database of Systematic Reviews, UpToDate, ProQuest Dissertations and Theses Global, and university archives. See APA 7, Section 9.30 for more information.

Found on an Open Access Website

Eaton, T. V., & Akers, M. D. (2007). Whistleblowing and good governance. CPA Journal , 77 (6), 66–71. http://archives.cpajournal.com/2007/607/essentials/p58.htm

Provide the direct web address/URL to a journal article found on the open web, often on an open access journal's website. In APA 7, active hyperlinks for DOIs and URLs should be used for documents meant for screen reading. Present these hyperlinks in blue and underlined text (the default formatting in Microsoft Word), although plain black text is also acceptable. Be consistent in your formatting choice for DOIs and URLs throughout your reference list.

Weinstein, J. A. (2010).  Social change  (3rd ed.). Rowman & Littlefield.

If the book has an edition number, include it in parentheses after the title of the book. If the book does not list any edition information, do not include an edition number. The edition number is not italicized.

American Nurses Association. (2015). Nursing: Scope and standards of practice (3rd ed.).

If the author and publisher are the same, only include the author in its regular place and omit the publisher.

Lencioni, P. (2012). The advantage: Why organizational health trumps everything else in business . Jossey-Bass. https://amzn.to/343XPSJ

As a change from APA 6 to APA 7, it is no longer necessary to include the ebook format in the title. However, if you listened to an audiobook and the content differs from the text version (e.g., abridged content) or your discussion highlights elements of the audiobook (e.g., narrator's performance), then note that it is an audiobook in the title element in brackets. For ebooks and online audiobooks, also include the DOI number (if available) or nondatabase URL but leave out the electronic retrieval element if the ebook was found in a common academic research database, as with journal articles. APA 7 allows for the shortening of long DOIs and URLs, as shown in this example. See APA 7, Section 9.36 for more information.

Chapter in an Edited Book

Poe, M. (2017). Reframing race in teaching writing across the curriculum. In F. Condon & V. A. Young (Eds.), Performing antiracist pedagogy in rhetoric, writing, and communication (pp. 87–105). University Press of Colorado.

Include the page numbers of the chapter in parentheses after the book title.

Christensen, L. (2001). For my people: Celebrating community through poetry. In B. Bigelow, B. Harvey, S. Karp, & L. Miller (Eds.), Rethinking our classrooms: Teaching for equity and justice (Vol. 2, pp. 16–17). Rethinking Schools.

Also include the volume number or edition number in the parenthetical information after the book title when relevant.

Freud, S. (1961). The ego and the id. In J. Strachey (Ed.),  The standard edition of the complete psychological works of Sigmund Freud  (Vol. 19, pp. 3-66). Hogarth Press. (Original work published 1923)

When a text has been republished as part of an anthology collection, after the author’s name include the date of the version that was read. At the end of the entry, place the date of the original publication inside parenthesis along with the note “original work published.” For in-text citations of republished work, use both dates in the parenthetical citation, original date first with a slash separating the years, as in this example: Freud (1923/1961). For more information on reprinted or republished works, see APA 7, Sections 9.40-9.41.

Classroom Resources

Citing classroom resources.

If you need to cite content found in your online classroom, use the author (if there is one listed), the year of publication (if available), the title of the document, and the main URL of Walden classrooms. For example, you are citing study notes titled "Health Effects of Exposure to Forest Fires," but you do not know the author's name, your reference entry will look like this:

Health effects of exposure to forest fires [Lecture notes]. (2005). Walden University Canvas. https://waldenu.instructure.com

If you do know the author of the document, your reference will look like this:

Smith, A. (2005). Health effects of exposure to forest fires [PowerPoint slides]. Walden University Canvas. https://waldenu.instructure.com  

A few notes on citing course materials:

• [Lecture notes]
• [Course handout]
• [Study notes]
• It can be difficult to determine authorship of classroom documents. If an author is listed on the document, use that. If the resource is clearly a product of Walden (such as the course-based videos), use Walden University as the author. If you are unsure or if no author is indicated, place the title in the author spot, as above.
• If you cannot determine a date of publication, you can use n.d. (for "no date") in place of the year.

Note:  The web location for Walden course materials is not directly retrievable without a password, and therefore, following APA guidelines, use the main URL for the class sites: https://class.waldenu.edu.

Citing Tempo Classroom Resources

Clear author: 

Smith, A. (2005). Health effects of exposure to forest fires [PowerPoint slides]. Walden University Brightspace. https://mytempo.waldenu.edu

Unclear author:

Health effects of exposure to forest fires [Lecture notes]. (2005). Walden University Brightspace. https://mytempo.waldenu.edu

Conference Sessions and Presentations

Feinman, Y. (2018, July 27). Alternative to proctoring in introductory statistics community college courses [Poster presentation]. Walden University Research Symposium, Minneapolis, MN, United States. https://scholarworks.waldenu.edu/symposium2018/23/

Torgerson, K., Parrill, J., & Haas, A. (2019, April 5-9). Tutoring strategies for online students [Conference session]. The Higher Learning Commission Annual Conference, Chicago, IL, United States. http://onlinewritingcenters.org/scholarship/torgerson-parrill-haas-2019/

Dictionary Entry

Merriam-Webster. (n.d.). Leadership. In Merriam-Webster.com dictionary . Retrieved May 28, 2020, from https://www.merriam-webster.com/dictionary/leadership

When constructing a reference for an entry in a dictionary or other reference work that has no byline (i.e., no named individual authors), use the name of the group—the institution, company, or organization—as author (e.g., Merriam Webster, American Psychological Association, etc.). The name of the entry goes in the title position, followed by "In" and the italicized name of the reference work (e.g., Merriam-Webster.com dictionary , APA dictionary of psychology ). In this instance, APA 7 recommends including a retrieval date as well for this online source since the contents of the page change over time. End the reference entry with the specific URL for the defined word.

Discussion Board Post

Osborne, C. S. (2010, June 29). Re: Environmental responsibility [Discussion post]. Walden University Canvas.  https://waldenu.instructure.com  

Dissertations or Theses

Retrieved From a Database

Nalumango, K. (2019). Perceptions about the asylum-seeking process in the United States after 9/11 (Publication No. 13879844) [Doctoral dissertation, Walden University]. ProQuest Dissertations and Theses.

Retrieved From an Institutional or Personal Website

Evener. J. (2018). Organizational learning in libraries at for-profit colleges and universities [Doctoral dissertation, Walden University]. ScholarWorks. https://scholarworks.waldenu.edu/cgi/viewcontent.cgi?article=6606&context=dissertations

Unpublished Dissertation or Thesis

Kirwan, J. G. (2005). An experimental study of the effects of small-group, face-to-face facilitated dialogues on the development of self-actualization levels: A movement towards fully functional persons [Unpublished doctoral dissertation]. Saybrook Graduate School and Research Center.

For further examples and information, see APA 7, Section 10.6.

Legal Material

For legal references, APA follows the recommendations of The Bluebook: A Uniform System of Citation , so if you have any questions beyond the examples provided in APA, seek out that resource as well.

Court Decisions

Reference format:

Name v. Name, Volume Reporter Page (Court Date). URL

Sample reference entry:

Brown v. Board of Education, 347 U.S. 483 (1954). https://www.oyez.org/cases/1940-1955/347us483

Sample citation:

In Brown v. Board of Education (1954), the Supreme Court ruled racial segregation in schools unconstitutional.

Note: Italicize the case name when it appears in the text of your paper.

Name of Act, Title Source § Section Number (Year). URL

Sample reference entry for a federal statute:

Individuals With Disabilities Education Act, 20 U.S.C. § 1400 et seq. (2004). https://www.congress.gov/108/plaws/publ446/PLAW-108publ446.pdf

Sample reference entry for a state statute:

Minnesota Nurse Practice Act, Minn. Stat. §§ 148.171 et seq. (2019). https://www.revisor.mn.gov/statutes/cite/148.171

Sample citation: Minnesota nurses must maintain current registration in order to practice (Minnesota Nurse Practice Act, 2010).

Note: The § symbol stands for "section." Use §§ for sections (plural). To find this symbol in Microsoft Word, go to "Insert" and click on Symbol." Look in the Latin 1-Supplement subset. Note: U.S.C. stands for "United States Code." Note: The Latin abbreviation " et seq. " means "and what follows" and is used when the act includes the cited section and ones that follow. Note: List the chapter first followed by the section or range of sections.

Unenacted Bills and Resolutions

(Those that did not pass and become law)

Title [if there is one], bill or resolution number, xxx Cong. (year). URL

Sample reference entry for Senate bill:

Anti-Phishing Act, S. 472, 109th Cong. (2005). https://www.congress.gov/bill/109th-congress/senate-bill/472

Sample reference entry for House of Representatives resolution:

Anti-Phishing Act, H.R. 1099, 109th Cong. (2005). https://www.congress.gov/bill/109th-congress/house-bill/1099

The Anti-Phishing Act (2005) proposed up to 5 years prison time for people running Internet scams.

These are the three legal areas you may be most apt to cite in your scholarly work. For more examples and explanation, see APA 7, Chapter 11.

Magazine Article

Clay, R. (2008, June). Science vs. ideology: Psychologists fight back about the misuse of research. Monitor on Psychology , 39 (6). https://www.apa.org/monitor/2008/06/ideology

Note that for citations, include only the year: Clay (2008). For magazine articles retrieved from a common academic research database, leave out the URL. For magazine articles from an online news website that is not an online version of a print magazine, follow the format for a webpage reference list entry.

Newspaper Article (Retrieved Online)

Baker, A. (2014, May 7). Connecticut students show gains in national tests. New York Times . http://www.nytimes.com/2014/05/08/nyregion/national-assessment-of-educational-progress-results-in-Connecticut-and-New-Jersey.html

Include the full date in the format Year, Month Day. Do not include a retrieval date for periodical sources found on websites. Note that for citations, include only the year: Baker (2014). For newspaper articles retrieved from a common academic research database, leave out the URL. For newspaper articles from an online news website that is not an online version of a print newspaper, follow the format for a webpage reference list entry.

Online Video/Webcast

Walden University. (2013).  An overview of learning  [Video]. Walden University Canvas.  https://waldenu.instructure.com  

Use this format for online videos such as Walden videos in classrooms. Most of our classroom videos are produced by Walden University, which will be listed as the author in your reference and citation. Note: Some examples of audiovisual materials in the APA manual show the word “Producer” in parentheses after the producer/author area. In consultation with the editors of the APA manual, we have determined that parenthetical is not necessary for the videos in our courses. The manual itself is unclear on the matter, however, so either approach should be accepted. Note that the speaker in the video does not appear in the reference list entry, but you may want to mention that person in your text. For instance, if you are viewing a video where Tobias Ball is the speaker, you might write the following: Tobias Ball stated that APA guidelines ensure a consistent presentation of information in student papers (Walden University, 2013). For more information on citing the speaker in a video, see our page on Common Citation Errors .

Taylor, R. [taylorphd07]. (2014, February 27). Scales of measurement [Video]. YouTube. https://www.youtube.com/watch?v=PDsMUlexaMY

Walden University Academic Skills Center. (2020, April 15). One-way ANCOVA: Introduction [Video]. YouTube. https://youtu.be/_XnNDQ5CNW8

For videos from streaming sites, use the person or organization who uploaded the video in the author space to ensure retrievability, whether or not that person is the speaker in the video. A username can be provided in square brackets. As a change from APA 6 to APA 7, include the publisher after the title, and do not use "Retrieved from" before the URL. See APA 7, Section 10.12 for more information and examples.

See also reference list entry formats for TED Talks .

Technical and Research Reports

Edwards, C. (2015). Lighting levels for isolated intersections: Leading to safety improvements (Report No. MnDOT 2015-05). Center for Transportation Studies. http://www.cts.umn.edu/Publications/ResearchReports/reportdetail.html?id=2402

Technical and research reports by governmental agencies and other research institutions usually follow a different publication process than scholarly, peer-reviewed journals. However, they present original research and are often useful for research papers. Sometimes, researchers refer to these types of reports as gray literature , and white papers are a type of this literature. See APA 7, Section 10.4 for more information.

Reference list entires for TED Talks follow the usual guidelines for multimedia content found online. There are two common places to find TED talks online, with slightly different reference list entry formats for each.

TED Talk on the TED website

If you find the TED Talk on the TED website, follow the format for an online video on an organizational website:

Owusu-Kesse, K. (2020, June). 5 needs that any COVID-19 response should meet [Video]. TED Conferences. https://www.ted.com/talks/kwame_owusu_kesse_5_needs_that_any_covid_19_response_should_meet

The speaker is the author in the reference list entry if the video is posted on the TED website. For citations, use the speaker's surname.

TED Talk on YouTube

If you find the TED Talk on YouTube or another streaming video website, follow the usual format for streaming video sites:

TED. (2021, February 5). The shadow pandemic of domestic violence during COVID-19 | Kemi DaSilvalbru [Video]. YouTube. https://www.youtube.com/watch?v=PGdID_ICFII

TED is the author in the reference list entry if the video is posted on YouTube since it is the channel on which the video is posted. For citations, use TED as the author.

Walden University Course Catalog

To include the Walden course catalog in your reference list, use this format:

Walden University. (2020). 2019-2020 Walden University catalog . https://catalog.waldenu.edu/index.php

If you cite from a specific portion of the catalog in your paper, indicate the appropriate section and paragraph number in your text:

...which reflects the commitment to social change expressed in Walden University's mission statement (Walden University, 2020, Vision, Mission, and Goals section, para. 2).

And in the reference list:

Walden University. (2020). Vision, mission, and goals. In 2019-2020 Walden University catalog. https://catalog.waldenu.edu/content.php?catoid=172&navoid=59420&hl=vision&returnto=search

Vartan, S. (2018, January 30). Why vacations matter for your health . CNN. https://www.cnn.com/travel/article/why-vacations-matter/index.html

For webpages on the open web, include the author, date, webpage title, organization/site name, and URL. (There is a slight variation for online versions of print newspapers or magazines. For those sources, follow the models in the previous sections of this page.)

American Federation of Teachers. (n.d.). Community schools . http://www.aft.org/issues/schoolreform/commschools/index.cfm

If there is no specified author, then use the organization’s name as the author. In such a case, there is no need to repeat the organization's name after the title.

In APA 7, active hyperlinks for DOIs and URLs should be used for documents meant for screen reading. Present these hyperlinks in blue and underlined text (the default formatting in Microsoft Word), although plain black text is also acceptable. Be consistent in your formatting choice for DOIs and URLs throughout your reference list.

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Home / Guides / Citation Guides / How to Cite Sources

How to Cite Sources

Here is a complete list for how to cite sources. Most of these guides present citation guidance and examples in MLA, APA, and Chicago.

If you’re looking for general information on MLA or APA citations , the EasyBib Writing Center was designed for you! It has articles on what’s needed in an MLA in-text citation , how to format an APA paper, what an MLA annotated bibliography is, making an MLA works cited page, and much more!

MLA Format Citation Examples

The Modern Language Association created the MLA Style, currently in its 9th edition, to provide researchers with guidelines for writing and documenting scholarly borrowings.  Most often used in the humanities, MLA style (or MLA format ) has been adopted and used by numerous other disciplines, in multiple parts of the world.

MLA provides standard rules to follow so that most research papers are formatted in a similar manner. This makes it easier for readers to comprehend the information. The MLA in-text citation guidelines, MLA works cited standards, and MLA annotated bibliography instructions provide scholars with the information they need to properly cite sources in their research papers, articles, and assignments.

• Book Chapter
• Conference Paper
• Documentary
• Encyclopedia
• Google Images
• Kindle Book
• Memorial Inscription
• Museum Exhibit
• Painting or Artwork
• PowerPoint Presentation
• Sheet Music
• Thesis or Dissertation
• YouTube Video

APA Format Citation Examples

The American Psychological Association created the APA citation style in 1929 as a way to help psychologists, anthropologists, and even business managers establish one common way to cite sources and present content.

APA is used when citing sources for academic articles such as journals, and is intended to help readers better comprehend content, and to avoid language bias wherever possible. The APA style (or APA format ) is now in its 7th edition, and provides citation style guides for virtually any type of resource.

Chicago Style Citation Examples

The Chicago/Turabian style of citing sources is generally used when citing sources for humanities papers, and is best known for its requirement that writers place bibliographic citations at the bottom of a page (in Chicago-format footnotes ) or at the end of a paper (endnotes).

The Turabian and Chicago citation styles are almost identical, but the Turabian style is geared towards student published papers such as theses and dissertations, while the Chicago style provides guidelines for all types of publications. This is why you’ll commonly see Chicago style and Turabian style presented together. The Chicago Manual of Style is currently in its 17th edition, and Turabian’s A Manual for Writers of Research Papers, Theses, and Dissertations is in its 8th edition.

Citing Specific Sources or Events

• Declaration of Independence
• Gettysburg Address
• Martin Luther King Jr. Speech
• President Obama’s Farewell Address
• President Trump’s Inauguration Speech
• White House Press Briefing

Additional FAQs

• Citing Archived Contributors
• Citing a Blog
• Citing a Book Chapter
• Citing a Source in a Foreign Language
• Citing an Image
• Citing a Song
• Citing Special Contributors
• Citing a Translated Article
• Citing a Tweet

6 Interesting Citation Facts

The world of citations may seem cut and dry, but there’s more to them than just specific capitalization rules, MLA in-text citations , and other formatting specifications. Citations have been helping researches document their sources for hundreds of years, and are a great way to learn more about a particular subject area.

Ever wonder what sets all the different styles apart, or how they came to be in the first place? Read on for some interesting facts about citations!

1. There are Over 7,000 Different Citation Styles

You may be familiar with MLA and APA citation styles, but there are actually thousands of citation styles used for all different academic disciplines all across the world. Deciding which one to use can be difficult, so be sure to ask you instructor which one you should be using for your next paper.

2. Some Citation Styles are Named After People

While a majority of citation styles are named for the specific organizations that publish them (i.e. APA is published by the American Psychological Association, and MLA format is named for the Modern Language Association), some are actually named after individuals. The most well-known example of this is perhaps Turabian style, named for Kate L. Turabian, an American educator and writer. She developed this style as a condensed version of the Chicago Manual of Style in order to present a more concise set of rules to students.

3. There are Some Really Specific and Uniquely Named Citation Styles

How specific can citation styles get? The answer is very. For example, the “Flavour and Fragrance Journal” style is based on a bimonthly, peer-reviewed scientific journal published since 1985 by John Wiley & Sons. It publishes original research articles, reviews and special reports on all aspects of flavor and fragrance. Another example is “Nordic Pulp and Paper Research,” a style used by an international scientific magazine covering science and technology for the areas of wood or bio-mass constituents.

4. More citations were created on  EasyBib.com  in the first quarter of 2018 than there are people in California.

The US Census Bureau estimates that approximately 39.5 million people live in the state of California. Meanwhile, about 43 million citations were made on EasyBib from January to March of 2018. That’s a lot of citations.

5. “Citations” is a Word With a Long History

The word “citations” can be traced back literally thousands of years to the Latin word “citare” meaning “to summon, urge, call; put in sudden motion, call forward; rouse, excite.” The word then took on its more modern meaning and relevance to writing papers in the 1600s, where it became known as the “act of citing or quoting a passage from a book, etc.”

6. Citation Styles are Always Changing

The concept of citations always stays the same. It is a means of preventing plagiarism and demonstrating where you relied on outside sources. The specific style rules, however, can and do change regularly. For example, in 2018 alone, 46 new citation styles were introduced , and 106 updates were made to exiting styles. At EasyBib, we are always on the lookout for ways to improve our styles and opportunities to add new ones to our list.

Why Citations Matter

Here are the ways accurate citations can help your students achieve academic success, and how you can answer the dreaded question, “why should I cite my sources?”

They Give Credit to the Right People

Citing their sources makes sure that the reader can differentiate the student’s original thoughts from those of other researchers. Not only does this make sure that the sources they use receive proper credit for their work, it ensures that the student receives deserved recognition for their unique contributions to the topic. Whether the student is citing in MLA format , APA format , or any other style, citations serve as a natural way to place a student’s work in the broader context of the subject area, and serve as an easy way to gauge their commitment to the project.

They Provide Hard Evidence of Ideas

Having many citations from a wide variety of sources related to their idea means that the student is working on a well-researched and respected subject. Citing sources that back up their claim creates room for fact-checking and further research . And, if they can cite a few sources that have the converse opinion or idea, and then demonstrate to the reader why they believe that that viewpoint is wrong by again citing credible sources, the student is well on their way to winning over the reader and cementing their point of view.

They Promote Originality and Prevent Plagiarism

The point of research projects is not to regurgitate information that can already be found elsewhere. We have Google for that! What the student’s project should aim to do is promote an original idea or a spin on an existing idea, and use reliable sources to promote that idea. Copying or directly referencing a source without proper citation can lead to not only a poor grade, but accusations of academic dishonesty. By citing their sources regularly and accurately, students can easily avoid the trap of plagiarism , and promote further research on their topic.

They Create Better Researchers

By researching sources to back up and promote their ideas, students are becoming better researchers without even knowing it! Each time a new source is read or researched, the student is becoming more engaged with the project and is developing a deeper understanding of the subject area. Proper citations demonstrate a breadth of the student’s reading and dedication to the project itself. By creating citations, students are compelled to make connections between their sources and discern research patterns. Each time they complete this process, they are helping themselves become better researchers and writers overall.

When is the Right Time to Start Making Citations?

Make in-text/parenthetical citations as you need them.

As you are writing your paper, be sure to include references within the text that correspond with references in a works cited or bibliography. These are usually called in-text citations or parenthetical citations in MLA and APA formats. The most effective time to complete these is directly after you have made your reference to another source. For instance, after writing the line from Charles Dickens’ A Tale of Two Cities : “It was the best of times, it was the worst of times…,” you would include a citation like this (depending on your chosen citation style):

(Dickens 11).

This signals to the reader that you have referenced an outside source. What’s great about this system is that the in-text citations serve as a natural list for all of the citations you have made in your paper, which will make completing the works cited page a whole lot easier. After you are done writing, all that will be left for you to do is scan your paper for these references, and then build a works cited page that includes a citation for each one.

Need help creating an MLA works cited page ? Try the MLA format generator on EasyBib.com! We also have a guide on how to format an APA reference page .

2. Understand the General Formatting Rules of Your Citation Style Before You Start Writing

While reading up on paper formatting may not sound exciting, being aware of how your paper should look early on in the paper writing process is super important. Citation styles can dictate more than just the appearance of the citations themselves, but rather can impact the layout of your paper as a whole, with specific guidelines concerning margin width, title treatment, and even font size and spacing. Knowing how to organize your paper before you start writing will ensure that you do not receive a low grade for something as trivial as forgetting a hanging indent.

Don’t know where to start? Here’s a formatting guide on APA format .

3. Double-check All of Your Outside Sources for Relevance and Trustworthiness First

Collecting outside sources that support your research and specific topic is a critical step in writing an effective paper. But before you run to the library and grab the first 20 books you can lay your hands on, keep in mind that selecting a source to include in your paper should not be taken lightly. Before you proceed with using it to backup your ideas, run a quick Internet search for it and see if other scholars in your field have written about it as well. Check to see if there are book reviews about it or peer accolades. If you spot something that seems off to you, you may want to consider leaving it out of your work. Doing this before your start making citations can save you a ton of time in the long run.

Finished with your paper? It may be time to run it through a grammar and plagiarism checker , like the one offered by EasyBib Plus. If you’re just looking to brush up on the basics, our grammar guides  are ready anytime you are.

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Purdue Online Writing Lab Purdue OWL® College of Liberal Arts

Reference List: Basic Rules

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Copyright ©1995-2018 by The Writing Lab & The OWL at Purdue and Purdue University. All rights reserved. This material may not be published, reproduced, broadcast, rewritten, or redistributed without permission. Use of this site constitutes acceptance of our terms and conditions of fair use.

This resourse, revised according to the 7 th  edition APA Publication Manual, offers basic guidelines for formatting the reference list at the end of a standard APA research paper. Most sources follow fairly straightforward rules. However, because sources obtained from academic journals  carry special weight in research writing, these sources are subject to special rules . Thus, this page presents basic guidelines for citing academic journals separate from its "ordinary" basic guidelines. This distinction is made clear below.

Note:  Because the information on this page pertains to virtually all citations, we've highlighted one important difference between APA 6 and APA 7 with an underlined note written in red.  For more information, please consult the   Publication Manual of the American Psychological Association , (7 th  ed.).

Formatting a Reference List

Your reference list should appear at the end of your paper. It provides the information necessary for a reader to locate and retrieve any source you cite in the body of the paper. Each source you cite in the paper must appear in your reference list; likewise, each entry in the reference list must be cited in your text.

Your references should begin on a new page separate from the text of the essay; label this page "References" in bold, centered at the top of the page (do NOT underline or use quotation marks for the title). All text should be double-spaced just like the rest of your essay.

Basic Rules for Most Sources

• All lines after the first line of each entry in your reference list should be indented one-half inch from the left margin. This is called hanging indentation.
• All authors' names should be inverted (i.e., last names should be provided first).
• For example, the reference entry for a source written by Jane Marie Smith would begin with "Smith, J. M."
• If a middle name isn't available, just initialize the author's first name: "Smith, J."
• Give the last name and first/middle initials for all authors of a particular work up to and including 20 authors ( this is a new rule, as APA 6 only required the first six authors ). Separate each author’s initials from the next author in the list with a comma. Use an ampersand (&) before the last author’s name. If there are 21 or more authors, use an ellipsis (but no ampersand) after the 19th author, and then add the final author’s name.
• Reference list entries should be alphabetized by the last name of the first author of each work.
• For multiple articles by the same author, or authors listed in the same order, list the entries in chronological order, from earliest to most recent.
• Note again that the titles of academic journals are subject to special rules. See section below.
• Italicize titles of longer works (e.g., books, edited collections, names of newspapers, and so on).
• Do not italicize, underline, or put quotes around the titles of shorter works such as chapters in books or essays in edited collections.

Basic Rules for Articles in Academic Journals

• Present journal titles in full.
• Italicize journal titles.
• For example, you should use  PhiloSOPHIA  instead of  Philosophia,  or  Past & Present   instead of  Past and Present.
• This distinction is based on the type of source being cited. Academic journal titles have all major words capitalized, while other sources' titles do not.
• Capitalize   the first word of the titles and subtitles of   journal articles , as well as the   first word after a colon or a dash in the title, and   any proper nouns .
• Do not italicize or underline the article title.
• Deep blue: The mysteries of the Marianas Trench.
• Oceanographic Study: A Peer-Reviewed Publication

Please note:  While the APA manual provides examples of how to cite common types of sources, it does not cover all conceivable sources. If you must cite a source that APA does not address, the APA suggests finding an example that is similar to your source and using that format. For more information, see page 282 of the   Publication Manual of the American Psychological Association , 7 th  ed.

Want to create or adapt books like this? Learn more about how Pressbooks supports open publishing practices.

13.3 Creating a References Section

Learning objective.

• Apply American Psychological Association (APA) style and formatting guidelines for a references section.

This section provides detailed information about how to create the references section of your paper. You will review basic formatting guidelines and learn how to format bibliographical entries for various types of sources. This section of Chapter 13 “APA and MLA Documentation and Formatting” , like the previous section, is meant to be used as a reference tool while you write.

Formatting the References Section: The Basics

At this stage in the writing process, you may already have begun setting up your references section. This section may consist of a single page for a brief research paper or may extend for many pages in professional journal articles. As you create this section of your paper, follow the guidelines provided here.

Formatting the References Section

To set up your references section, use the insert page break feature of your word-processing program to begin a new page. Note that the header and margins will be the same as in the body of your paper, and pagination continues from the body of your paper. (In other words, if you set up the body of your paper correctly, the correct header and page number should appear automatically in your references section.) See additional guidelines below.

Formatting Reference Entries

Reference entries should include the following information:

• The name of the author(s)
• The year of publication and, where applicable, the exact date of publication
• The full title of the source
• For books, the city of publication
• For articles or essays, the name of the periodical or book in which the article or essay appears
• For magazine and journal articles, the volume number, issue number, and pages where the article appears
• For sources on the web, the URL where the source is located

See the following examples for how to format a book or journal article with a single author.

Sample Book Entry

Sample Journal Article Entry

The following box provides general guidelines for formatting the reference page. For the remainder of this chapter, you will learn about how to format bibliographical entries for different source types, including multiauthor and electronic sources.

Formatting the References Section: APA General Guidelines

1. Include the heading References , centered at the top of the page. The heading should not be boldfaced, italicized, or underlined. 2. Use double-spaced type throughout the references section, as in the body of your paper. 3. Use hanging indentation for each entry. The first line should be flush with the left margin, while any lines that follow should be indented five spaces. Note that hanging indentation is the opposite of normal indenting rules for paragraphs. 4. List entries in alphabetical order by the author’s last name. For a work with multiple authors, use the last name of the first author listed. 5. List authors’ names using this format: Smith, J. C. 6. For a work with no individual author(s), use the name of the organization that published the work or, if this is unavailable, the title of the work in place of the author’s name.

7. For works with multiple authors, follow these guidelines:

• For works with up to seven authors, list the last name and initials for each author.
• For works with more than seven authors, list the first six names, followed by ellipses, and then the name of the last author listed.
• Use an ampersand before the name of the last author listed.

8. Use title case for journal titles. Capitalize all important words in the title.

9. Use sentence case for all other titles—books, articles, web pages, and other source titles. Capitalize the first word of the title. Do not capitalize any other words in the title except for the following:

• Proper nouns
• First word of a subtitle
• First word after a colon or dash

Set up the first page of your references section and begin adding entries, following the APA formatting guidelines provided in this section.

• If there are any simple entries that you can format completely using the general guidelines, do so at this time.
• For entries you are unsure of how to format, type in as much information as you can, and highlight the entries so you can return to them later.

Formatting Reference Entries for Different Source Types

As is the case for in-text citations, formatting reference entries becomes more complicated when you are citing a source with multiple authors, citing various types of online media, or citing sources for which you must provide additional information beyond the basics listed in the general guidelines. The following guidelines show how to format reference entries for these different situations.

Print Sources: Books

For book-length sources and shorter works that appear in a book, follow the guidelines that best describes your source.

A Book by Two or More Authors

List the authors’ names in the order they appear on the book’s title page. Use an ampersand before the last author’s name.

Campbell, D. T., & Stanley, J. C. (1963). Experimental and quasi-experimental designs for research. Boston, MA: Houghton Mifflin.

An Edited Book with No Author

List the editor or editors’ names in place of the author’s name, followed by Ed. or Eds. in parentheses.

Myers, C., & Reamer, D. (Eds.). (2009). 2009 nutrition index. San Francisco, CA: HealthSource, Inc.

An Edited Book with an Author

List the author’s name first, followed by the title and the editor or editors. Note that when the editor is listed after the title, you list the initials before the last name.

The previous example shows the format used for an edited book with one author—for instance, a collection of a famous person’s letters that has been edited. This type of source is different from an anthology, which is a collection of articles or essays by different authors. For citing works in anthologies, see the guidelines later in this section.

A Translated Book

Include the translator’s name after the title, and at the end of the citation, list the date the original work was published. Note that for the translator’s name, you list the initials before the last name.

Freud, S. (1965). New introductory lectures on psycho-analysis (J. Strachey, Trans.). New York, NY: W. W. Norton. (Original work published 1933).

A Book Published in Multiple Editions

If you are using any edition other than the first edition, include the edition number in parentheses after the title.

A Chapter in an Edited Book

List the name of the author(s) who wrote the chapter, followed by the chapter title. Then list the names of the book editor(s) and the title of the book, followed by the page numbers for the chapter and the usual information about the book’s publisher.

A Work That Appears in an Anthology

Follow the same process you would use to cite a book chapter, substituting the article or essay title for the chapter title.

An Article in a Reference Book

List the author’s name if available; if no author is listed, provide the title of the entry where the author’s name would normally be listed. If the book lists the name of the editor(s), include it in your citation. Indicate the volume number (if applicable) and page numbers in parentheses after the article title.

Two or More Books by the Same Author

List the entries in order of their publication year, beginning with the work published first.

Swedan, N. (2001). Women’s sports medicine and rehabilitation. Gaithersburg, MD: Aspen Publishers.

Swedan, N. (2003). The active woman’s health and fitness handbook. New York, NY: Perigee.

If two books have multiple authors, and the first author is the same but the others are different, alphabetize by the second author’s last name (or the third or fourth, if necessary).

Carroll, D., & Aaronson, F. (2008). Managing type II diabetes. Chicago, IL: Southwick Press.

Carroll, D., & Zuckerman, N. (2008). Gestational diabetes. Chicago, IL: Southwick Press.

Books by Different Authors with the Same Last Name

Alphabetize entries by the authors’ first initial.

A Book Authored by an Organization

Treat the organization name as you would an author’s name. For the purposes of alphabetizing, ignore words like The in the organization’s name. (That is, a book published by the American Heart Association would be listed with other entries whose authors’ names begin with A .)

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders DSM-IV (4th ed.). Arlington, VA: American Psychiatric Publishing.

A Book-Length Report

Format technical and research reports as you would format other book-length sources. If the organization that issued the report assigned it a number, include the number in parentheses after the title. (See also the guidelines provided for citing works produced by government agencies.)

Jameson, R., & Dewey, J. (2009). Preliminary findings from an evaluation of the president’s physical fitness program in Pleasantville school district. Pleasantville, WA: Pleasantville Board of Education.

A Book Authored by a Government Agency

Treat these as you would a book published by a nongovernment organization, but be aware that these works may have an identification number listed. If so, include it in parentheses after the publication year.

U.S. Census Bureau. (2002). The decennial censuses from 1790 to 2000 (Publication No. POL/02-MA). Washington, DC: US Government Printing Offices.

Revisit the references section you began to compile in Note 13.73 “Exercise 1” . Use the guidelines provided to format any entries for book-length print sources that you were unable to finish earlier.

Review how Jorge formatted these book-length print sources:

Atkins, R. C. (2002). Dr. Atkins’ diet revolution . New York, NY: M. Evans and Company.

Agatson, A. (2003). The South Beach diet. New York, NY: St. Martin’s Griffin.

Print Sources: Periodicals

An article in a scholarly journal.

Include the following information:

• Author or authors’ names
• Publication year
• Article title (in sentence case, without quotation marks or italics)
• Journal title (in title case and in italics)
• Volume number (in italics)
• Issue number (in parentheses)
• Page number(s) where the article appears

DeMarco, R. F. (2010). Palliative care and African American women living with HIV. Journal of Nursing Education, 49 (5), 1–4.

An Article in a Journal Paginated by Volume

In these types of journals, page numbers for one volume continue across all the issues in that volume. For instance, the winter issue may begin with page 1, and in the spring issue that follows, the page numbers pick up where the previous issue left off. (If you have ever wondered why a print journal did not begin on page 1, or wondered why the page numbers of a journal extend into four digits, this is why.) Omit the issue number from your reference entry.

Wagner, J. (2009). Rethinking school lunches: A review of recent literature. American School Nurses’ Journal , 47, 1123–1127.

An Abstract of a Scholarly Article

At times you may need to cite an abstract—the summary that appears at the beginning—of a published article. If you are citing the abstract only, and it was published separately from the article, provide the following information:

• Publication information for the article
• Information about where the abstract was published (for instance, another journal or a collection of abstracts)

A Journal Article with Two to Seven Authors

List all the authors’ names in the order they appear in the article. Use an ampersand before the last name listed.

Barker, E. T., & Bornstein, M. H. (2010). Global self-esteem, appearance satisfaction, and self-reported dieting in early adolescence. Journal of Early Adolescence, 30 (2), 205–224.

Tremblay, M. S., Shields, M., Laviolette, M., Craig, C. L., Janssen, I., & Gorber, S. C. (2010). Fitness of Canadian children and youth: Results from the 2007–2009 Canadian Health Measures Survey. Health Reports, 21 (1), 7–20.

A Journal Article with More Than Seven Authors

List the first six authors’ names, followed by a comma, an ellipsis, and the name of the last author listed. The article in the following example has sixteen listed authors; the reference entry lists the first six authors and the sixteenth, omitting the seventh through the fifteenth.

Writing at Work

The idea of an eight-page article with sixteen authors may seem strange to you—especially if you are in the midst of writing a ten-page research paper on your own. More often than not, articles in scholarly journals list multiple authors. Sometimes, the authors actually did collaborate on writing and editing the published article. In other instances, some of the authors listed may have contributed to the research in some way while being only minimally involved in the process of writing the article. Whenever you collaborate with colleagues to produce a written product, follow your profession’s conventions for giving everyone proper credit for their contribution.

A Magazine Article

After the publication year, list the issue date. Otherwise, treat these as you would journal articles. List the volume and issue number if both are available.

A Newspaper Article

Treat these as you would magazine and journal articles, with one important difference: precede the page number(s) with the abbreviation p. (for a single-page article) or pp. (for a multipage article). For articles whose pagination is not continuous, list all the pages included in the article. For example, an article that begins on page A1 and continues on pages A4 would have the page reference A1, A4. An article that begins on page A1 and continues on pages A4 and A5 would have the page reference A1, A4–A5.

A Letter to the Editor

After the title, indicate in brackets that the work is a letter to the editor.

Jones, J. (2009, January 31). Food police in our schools [Letter to the editor]. Rockwood Gazette, p. A8.

After the title, indicate in brackets that the work is a review and state the name of the work being reviewed. (Note that even if the title of the review is the same as the title of the book being reviewed, as in the following example, you should treat it as an article title. Do not italicize it.)

Revisit the references section you began to compile in Note 13.73 “Exercise 1” . Use the guidelines provided above to format any entries for periodicals and other shorter print sources that you were unable to finish earlier.

Electronic Sources

Citing articles from online periodicals: urls and digital object identifiers (dois).

Whenever you cite online sources, it is important to provide the most up-to-date information available to help readers locate the source. In some cases, this means providing an article’s URL , or web address. (The letters URL stand for uniform resource locator.) Always provide the most complete URL possible. Provide a link to the specific article used, rather than a link to the publication’s homepage.

As you know, web addresses are not always stable. If a website is updated or reorganized, the article you accessed in April may move to a different location in May. The URL you provided may become a dead link. For this reason, many online periodicals, especially scholarly publications, now rely on DOIs rather than URLs to keep track of articles.

A DOI is a Digital Object Identifier—an identification code provided for some online documents, typically articles in scholarly journals. Like a URL, its purpose is to help readers locate an article. However, a DOI is more stable than a URL, so it makes sense to include it in your reference entry when possible. Follow these guidelines:

• If you are citing an online article with a DOI, list the DOI at the end of the reference entry.
• If the article appears in print as well as online, you do not need to provide the URL. However, include the words Electronic version after the title in brackets.
• In other respects, treat the article as you would a print article. Include the volume number and issue number if available. (Note, however, that these may not be available for some online periodicals).

An Article from an Online Periodical with a DOI

List the DOI if one is provided. There is no need to include the URL if you have listed the DOI.

Bell, J. R. (2006). Low-carb beats low-fat diet for early losses but not long term. OBGYN News, 41 (12), 32. doi:10.1016/S0029-7437(06)71905-X

An Article from an Online Periodical with No DOI

List the URL. Include the volume and issue number for the periodical if this information is available. (For some online periodicals, it may not be.)

Note that if the article appears in a print version of the publication, you do not need to list the URL, but do indicate that you accessed the electronic version.

Robbins, K. (2010, March/April). Nature’s bounty: A heady feast [Electronic version]. Psychology Today, 43 (2), 58.

Provide the URL of the article.

McNeil, D. G. (2010, May 3). Maternal health: A new study challenges benefits of vitamin A for women and babies. The New York Times. Retrieved from http://www.nytimes.com/2010/05/04/health/04glob.html?ref=health

An Article Accessed through a Database

Cite these articles as you would normally cite a print article. Provide database information only if the article is difficult to locate.

APA style does not require writers to provide the item number or accession number for articles retrieved from databases. You may choose to do so if the article is difficult to locate or the database is an obscure one. Check with your professor to see if this is something he or she would like you to include.

An Abstract of an Article

Format these as you would an article citation, but add the word Abstract in brackets after the title.

Bradley, U., Spence, M., Courtney, C. H., McKinley, M. C., Ennis, C. N., McCance, D. R.…Hunter, S. J. (2009). Low-fat versus low-carbohydrate weight reduction diets: Effects on weight loss, insulin resistance, and cardiovascular risk: A randomized control trial [Abstract]. Diabetes , 58 (12), 2741–2748. http://diabetes.diabetesjournals.org/content/early/2009/08/23/db00098.abstract

A Nonperiodical Web Document

The ways you cite different nonperiodical web documents may vary slightly from source to source, depending on the information that is available. In your citation, include as much of the following information as you can:

• Name of the author(s), whether an individual or organization
• Date of publication (Use n.d. if no date is available.)
• Title of the document
• Address where you retrieved the document

If the document consists of more than one web page within the site, link to the homepage or the entry page for the document.

American Heart Association. (2010). Heart attack, stroke, and cardiac arrest warning signs. Retrieved from http://www.americanheart.org/presenter.jhtml?identifier=3053

An Entry from an Online Encyclopedia or Dictionary

Because these sources often do not include authors’ names, you may list the title of the entry at the beginning of the citation. Provide the URL for the specific entry.

Addiction. (n.d.) In Merriam-Webster’s online dictionary . Retrieved from http://www.merriam-webster.com/dictionary/addiction

If you cite raw data compiled by an organization, such as statistical data, provide the URL where you retrieved the information. Provide the name of the organization that sponsors the site.

US Food and Drug Administration. (2009). Nationwide evaluation of X-ray trends: NEXT surveys performed [Data file]. Retrieved from http://www.fda.gov/Radiation-EmittingProducts/RadiationSafety/NationwideEvaluationofX- RayTrendsNEXT/ucm116508.htm

Graphic Data

When citing graphic data—such as maps, pie charts, bar graphs, and so on—include the name of the organization that compiled the information, along with the publication date. Briefly describe the contents in brackets. Provide the URL where you retrieved the information. (If the graphic is associated with a specific project or document, list it after your bracketed description of the contents.)

US Food and Drug Administration. (2009). [Pie charts showing the percentage breakdown of the FDA’s budget for fiscal year 2005]. 2005 FDA budget summary . Retrieved from mhttp://www.fda.gov/AboutFDA/ReportsManualsForms/Reports/BudgetReports/2005FDABudgetSummary/ucm117231.htm

An Online Interview (Audio File or Transcript)

List the interviewer, interviewee, and date. After the title, include bracketed text describing the interview as an “Interview transcript” or “Interview audio file,” depending on the format of the interview you accessed. List the name of the website and the URL where you retrieved the information. Use the following format.

Davies, D. (Interviewer), & Pollan, M. (Interviewee). (2008). Michael Pollan offers president food for thought [Interview transcript]. Retrieved from National Public Radio website: http://www.npr.org/templates/transcript/transcript.php?storyId=100755362

An Electronic Book

Electronic books may include books available as text files online or audiobooks. If an electronic book is easily available in print, cite it as you would a print source. If it is unavailable in print (or extremely difficult to find), use the format in the example. (Use the words Available from in your citation if the book must be purchased or is not available directly.)

Chisholm, L. (n.d.). Celtic tales. Retrieved from http://www.childrenslibrary.org/icdl/BookReader?bookid= chicelt_00150014&twoPage=false&route=text&size=0&fullscreen=false&pnum1=1&lang= English&ilang=English

A Chapter from an Online Book or a Chapter or Section of a Web Document

These are treated similarly to their print counterparts with the addition of retrieval information. Include the chapter or section number in parentheses after the book title.

Hart, A. M. (1895). Restoratives—Coffee, cocoa, chocolate. In Diet in sickness and in health (VI). Retrieved from http://www.archive.org/details/dietinsicknessin00hartrich

A Dissertation or Thesis from a Database

Provide the author, date of publication, title, and retrieval information. If the work is numbered within the database, include the number in parentheses at the end of the citation.

Computer Software

For commonly used office software and programming languages, it is not necessary to provide a citation. Cite software only when you are using a specialized program, such as the nutrition tracking software in the following example. If you download software from a website, provide the version and the year if available.

Internet Brands, Inc. (2009). FitDay PC (Version 2) [Software]. Available from http://www.fitday.com/Pc/PcHome.html?gcid=14

A Post on a Blog or Video Blog

Citation guidelines for these sources are similar to those used for discussion forum postings. Briefly describe the type of source in brackets after the title.

Because the content may not be carefully reviewed for accuracy, discussion forums and blogs should not be relied upon as a major source of information. However, it may be appropriate to cite these sources for some types of research. You may also participate in discussion forums or comment on blogs that address topics of personal or professional interest. Always keep in mind that when you post, you are making your thoughts public—and in many cases, available through search engines. Make sure any posts that can easily be associated with your name are appropriately professional, because a potential employer could view them.

A Television or Radio Broadcast

Include the name of the producer or executive producer; the date, title, and type of broadcast; and the associated company and location.

West, Ty. (Executive producer). (2009, September 24). PBS special report: Health care reform [Television broadcast]. New York, NY, and Washington, DC: Public Broadcasting Service.

A Television or Radio Series or Episode

Include the producer and the type of series if you are citing an entire television or radio series.

Couture, D., Nabors, S., Pinkard, S., Robertson, N., & Smith, J. (Producers). (1979). The Diane Rehm show [Radio series]. Washington, DC: National Public Radio.

To cite a specific episode of a radio or television series, list the name of the writer or writers (if available), the date the episode aired, its title, and the type of series, along with general information about the series.

Bernanke, J., & Wade, C. (2010, January 10). Hummingbirds: Magic in the air [Television series episode]. In F. Kaufman (Executive producer), Nature. New York, NY: WNET.

A Motion Picture

Name the director or producer (or both), year of release, title, country of origin, and studio.

Spurlock, M. (Director/producer), Morley, J. (Executive producer), & Winters. H. M. (Executive producer). (2004). Super size me. United States: Kathbur Pictures in association with Studio on Hudson.

A Recording

Name the primary contributors and list their role. Include the recording medium in brackets after the title. Then list the location and the label.

Smith, L. W. (Speaker). (1999). Meditation and relaxation [CD]. New York, NY: Earth, Wind, & Sky Productions.

Székely, I. (Pianist), Budapest Symphony Orchestra (Performers), & Németh, G. (Conductor). (1988). Chopin piano concertos no. 1 and 2 [CD]. Hong Kong: Naxos.

Provide as much information as possible about the writer, director, and producer; the date the podcast aired; its title; any organization or series with which it is associated; and where you retrieved the podcast.

Kelsey, A. R. (Writer), Garcia, J. (Director), & Kim, S. C. (Producer). (2010, May 7). Lies food labels tell us. Savvy consumer podcasts [Audio podcast] . Retrieved from http://www.savvyconsumer.org/podcasts/050710

Revisit the references section you began to compile in Note 13.73 “Exercise 1” .

• Use the APA guidelines provided in this section to format any entries for electronic sources that you were unable to finish earlier.
• If your sources include a form of media not covered in the APA guidelines here, consult with a writing tutor or review a print or online reference book. You may wish to visit the website of the American Psychological Association at http://www.apa.org or the Purdue University Online Writing lab at http://owl.english.purdue.edu , which regularly updates its online style guidelines.
• Give your paper a final edit to check the references section.

Key Takeaways

In APA papers, entries in the references section include as much of the following information as possible:

• Print sources. Author(s), date of publication, title, publisher, page numbers (for shorter works), editors (if applicable), and periodical title (if applicable).
• Online sources (text-based). Author(s), date of publication, title, publisher or sponsoring organization, and DOI or URL (if applicable).
• Electronic sources (non-text-based). Provide details about the creator(s) of the work, title, associated company or series, and date the work was produced or broadcast. The specific details provided will vary depending on the medium and the information that is available.
• Electronic sources (text-based). If an electronic source is also widely available in print form, it is sometimes unnecessary to provide details about how to access the electronic version. Check the guidelines for the specific source type.

Writing for Success Copyright © 2015 by University of Minnesota is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

Educational resources and simple solutions for your research journey

How to Write References in Research Papers: Navigating the Maze (Part 2)

You truly are navigating a maze when it comes to ci tations and the question of how to write references in research pa per s. In part 1 of this article, we touched upon citations, which are pointers embedded in the text of a research paper, to sources of information or to other research relevant to that being described in the research paper. Those pointers lead to references in research papers , which typically appear at the end of the text. Whereas citations merely point us to sources in research papers, references describe those sources in sufficient detail for readers (1) to know the title of each source, who is responsible for its content, and when it was published; (2) to look up those sources; and (3) to obtain the documents in question if required.  

Table of Contents

Types of references in research papers

In writing a research paper, a researcher draws upon many sources of information, knowledge, opinions, and so on. One of the the most common type s of reference s  in research papers is other research papers published in journals; other common sources include technical reports, handbooks, presentations at conferences, and books. Increasingly, the sources in research papers are digital and include web pages, databases, blog posts, and even tweets and emails.  

Not all sources are considered equally credible , and some may not be accessible to all because they are behind paywalls or available only to members of a network (company intranets, for example) or because they are personal exchanges.  

How to write references in research papers

If the citations follow the Harvard system, references in a research paper s are sorted alphabetically by the last name of the first author; if the citations follow the Vancouver system, the references are arranged by numbers: the reference corresponding to the first numbered citation is numbered 1, and so on. If a source is cited again, its allocated number does not change.  

Some additional conventions govern the alphabetic sorting of references in research papers . For instance, when authors have some papers in which they are the only author and others in which they have one or more co-authors or when the same author or authors have papers published in different years or even within the same year.  

Some publishers make even greater demands of references in research papers : authors are expected to sort the list of references alphabetically, as in the Harvard system; then number the sorted list serially; and then renumber all the citations within the text so that each corresponds to its new number!  

How to add references in a research paper: Key elements

For a source of information to be described accurately, some minimum details are required. Here’s one example of w rit ing references in research paper s – ‘ Nature 171 : 737’ is a code that, if you know how to decipher it, tells you that it means an article published in Nature (a weekly journal published from the UK) that begins on page 737 of volume 171 of that journal. However, it does not tell you what the article was about, who wrote it, when it was published, or even how long it is. A complete reference in research paper s (Fig. 1), however, tells you that the title of the article was ‘Molecular structure of nucleic acids: a structure for deoxyribose nucleic acid’, that it was written by J. D. Watson and F. H. C. Crick, that it was published in 1953, and that it ran to no more than two pages.  

When thinking about how to write research references , remember that the elements that make up a reference to an article published in a journal are different from those that make up a reference to a book (edition if not the first, the publisher, and the place of publication, although the last is no longer considered essential in today’s globalized publishing). The elements that make up a reference to a technical report include the name of the organization issuing that report and the report number, if any, and that to a conference presentation gives the title of the conference, the date(s) on which it was held and the place, the name of the organizer(s) of the conference, and so on.  

Note that journals or publishers differ in the elements they expect authors to include when they state how to put references in research papers ; for example, some journals give only minimal information and exclude the titles of articles and some use the ‘elided’ form of page numbers (737–38 instead of 737–738, for example).  

Then there is the question of abbreviated names of journals: some publishers abbreviate journal titles and some don’t ( Annals of Applied Biology or Ann. Appl. Biol.). And those who do, often disagree on the correct abbreviation—and on whether the abbreviations should end in dots (whether the word ‘Journal’ should be given as J. or J or Jnl or Jnl.).  

Sequence of the elements that make up reference s in research papers  

Publishers and journals also differ in the order or sequence in which they present the elements or components of reference s in research papers : usually, British and European publishers put the year of publication after the names of authors whereas US publishers move the year closer to the volume number of the journal.  

Even within an element, the sequence of references in research paper s can have subtle differences. In Harvard system, because the last name of the first author is using for sorting, the name is ‘inverted’, that is the last name is given first, followed by initials (Watson J D instead of J D Watson). However, some journals invert the names of all the authors whereas some invert the name of only the first author. In Vancouver system, the names are seldom inverted because the sequence is not alphabetical.  

Punctuation to separate the elements that make up references in research papers

The many exasperating details that go into formatting references include punctuation marks (or their absence). In giving the initials of authors, some journals use dots, some journals use space, some use both, and some use neither (Watson J.D. or Watson J D or Watson J. D. or Watson JD). Some use a comma between the last name and the initials whereas some reserve the comma only to separate one name from the next (Watson, J D and Crick, F H C or Watson J D, Crick F H C). Some use ‘and’ some don’t, even when there are only two authors, and some use ‘&’ instead which makes it even more confusing for those struggling with how to write references in a research paper.

When the place of publication was a required element in the case of books, some publishers used the colon and some used the comma (and also changed the order, as in New York: Harper & Row or Harper & Row, New York). Some publishers end each reference with a full stop (period) and some don’t.

Typography of references in research papers  

As if the variations mentioned above were not enough, when figuring out how to add references in a research paper , you also have to contend with the differences in typography as well: journal titles in italics or in normal type, volume numbers in bold or in normal type, hyphens or en dashes between page numbers (737-738 or 737–738), and so on.  

All is not lost, however, if you despair of ever getting the references in a research paper right. For example, some publishers now insist on correct formatting only after a paper has been accepted for publication. Also, ICMJE, the International Committee of Medical Journal Editors, recommends a set of uniform requirements for manuscripts (the requirements include the formatting of citations and references), and hundreds of medical journals ( www.icmje.org/journals-following-the-icmje-recommendations/ ) have agreed that as long as authors adhere to those recommendations on how to mention references for research papers , any changes to the formatting any journal wants to make will be made by the journal in question.  

Lastly, several software packages help authors to automate this mundane task of consistent formatting of references in research paper s—but that is another article and another day.  

The details involved in using citations and references correctly can be overwhelming for some of us. While this article covers the key tips to help you understand how to give reference s in research paper s , be sure to check out article 1 of this two-part series for more on what, when and how to cite in a research paper. One way to check whether these are handled correctly in your manuscript is to use Researcher.Life’s AI powered manuscript optimizer , which can flag any discrepancies, departures from standard style, and mismatches between citations and references in research paper s.  

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Citing Sources: Sample Reference List Citations

• Style Links & Samples
• Sample Reference List Citations
• Sample Notes and Bibliography Citations
• Sample Author Date Citations
• Citing Nontraditional Sources in Chicago
• Sample Citations
• Major Changes to the New MLA
• Capitalization and Personal Names in Foreign Languages
• Citing Primary Sources
• Ancient Texts
• Citation Consultations Policy

When formatting a citation in APA style, pay particular attention to italics, punctuation, indentation, and capitalization.

Many more samples of citations presented in the APA style can be found in the Publication Manual of the American Psychological Association . Please consult this book or a librarian for help with unusual resources.

All of the following samples are taken from:

American Psychological Association. (2010). Publication manual of the American Psychological Association (6th ed.). Washington, DC: American Psychological Association.

(In the above sample, the name of the organization is the author. Note that only proper names are capitalized in the title, and the edition number follows the title.)

Book: (This sample from Purdue OWL )

Calfee, R. C., & Valencia, R. R. (1991).  APA guide to preparing manuscripts for journal publication . Washington, DC: American Psychological Association.

Book with an Editor:

Robinson, D. N. (Ed.). (1992). Social discourse and moral judgment . San Diego, CA: Academic Press.

Note: italicize the title of the book and do not capitalize any words in titles except the first word, proper names, and after a colon. Use the author's or editor's initials only for first and middle names.

Chapter from an Edited Volume or Anthology :

Haybron, D. M. (2008). Philosophy and the science of subjective well-being. In M. Eid & R. J. Larsen (Eds.),  The science of subjective well-being  (pp. 17-43). New York, NY: Guilford Press. 

Scholarly Article:

Fuentes, A. (2016). Contemporary evolutionary theory in biological anthropology: Insight into human evolution,  genomics  and challenges to  racialized  pseudo-science.   Revista   Cuicuilco , 23 (65), 293-304. 

Note: Do not set off the title of the article with quotes, italics, underlines, or capital letters (except for the first word, proper names or after a colon). Italicize the title of the journal and capitalize all words in the title of the journal. This sample includes the volume number (23) which is italicized to set it off from the other numbers. The issue number (65) appears in parentheses and is not italicized. You will also notice that there is no space left between the volume number and the first parenthesis for the issue number.

Scholarly Article (with multiple authors):

Calvo, M. G., & Lang, P. J. (2004). Gaze patterns when looking at emotional pictures: Motivationally biased attention. Motivation and Emotion, 28 , 221-243. https://doi.org/10.1023/B:MOEM.0000040153.26156.ed

Note: This sample includes the volume number (28), which is italicized to set it off from the page numbers. There is no issue number in this example because the journal is paginated by volume. Provide the DOI when available for electronic documents. If a DOI is not available for a scholarly article retrieved online, you should supply the URL of the journal's homepage (NOT the URL from the database). Note authors' names, indentations, spare use of capital letters, page numbers, and use of periods and commas.

Popular Article (with two authors):

Kandel, E. R., & Squire, L. R. (2000, November 10). Neuroscience: Breaking down scientific barriers to the study of brain and mind. Science, 290, 1113-1120.

Note: Do not set off the title of the article with quotes, italics, underlines, or capital letters (except for the first word, proper names, or after a colon). Italicize the title of the magazine and capitalize all keywords in the title. Italicize the volume number to set it off from the page numbers.

Newspaper Article:

Scwartz, J. (1993, September 30). Obesity affects economic, social status. The Washington Post , pp. A1, A4.

Note: Do not set off the title of the article with quotes, italics, underlines, or capital letters (except for the first word, proper names or after a colon). Italicize the title of the newspaper and capitalize all keywords in the title of the newspaper.

Webpage Examples:  (These samples from  Purdue OWL )

Author, A. A. & Author B. B. (Date of publication ,  or  n. d. if no date ). Title of page [Format description when necessary]. Retrieved from https://www.someaddress.com/full/url/

Eco, U. (2015). How to write a thesis [PDF file]. (Farina C. M. & Farina F., Trans.) Retrieved from https://www.researchgate.net/...How_to_write_a_thesis/.../Umberto+Eco-How+to+Write+... (Original work published 1977).

If the page's author is not listed, start with the title. If the date of publication is not listed, use the abbreviation (n.d.):

Spotlight Resources. (n.d.). Retrieved from https://owl.purdue.edu/owl/about_the_owl/owl_information/spotlight_resources.html

Only include a date of access when page content is likely to change over time (ex: if you're citing a wiki):

Purdue University Writing Lab [Facebook page]. (n.d.). Retrieved January 22, 2019, from https://www.facebook.com/PurdueUniversityWritingLab/

Nonperiodical Web Document or Report (Examples: government data such as U.S. Census): (This sample from Purdue OWL )

Author, A. A., & Author, B. B. (Date of publication, or n.d. if no date).  Title of document . Retrieved from https://Web address

Angeli, E., Wagner, J., Lawrick, E., Moore, K., Anderson, M., Soderland, L., & Brizee, A. (2010, May 5).  General format.  Retrieved from http://owl.english.purdue.edu/owl/resource/560/01/

Note: Italicize the title of the website but do not capitalize any words except the first, proper names, and the first word following a colon.

For citing company or industry reports from the library's MarketLine database, also see:

https://guides.library.ualberta.ca/apa-citation-style/business

Publication manual of the American Psychological Association 7.07

If map is within a book, cite as In Title of book after [Type of map].

Cite primary contributors in the Author's space followed by their contributing role in parentheses.

Other forms for [Type of map] include:

• [Demographic map]
• [Topographical map]

Use (n.d.) for No date.

Title of map. (Year). [Type of Map]. Publisher Location: Publisher.

Citation Examples:

Plattsburgh, Clinton County: Dannemora, Peru, Keeseville, Champlain, Rouses Point, New York State, 3rd ed.

(1999). [Road map]. Clifton Park, NY: Jimapco.

Topographical Map:

Berlin, N.Y. - Mass. - VT. (1988). [Topographical map]. reston, VA: U.S. Geological Survey.

Online Map:

Follow the map citation guidelines as above, but also include a stable URL where the map is found.

Title of map. (Year). [Type of map]. Retrieved from http://xxx.xx

Manhattan sightseeing map. (2010). [City map]. Retrieved from http://www.ny.com/maps/shopmap.html

MTA Metro-North railroad. (2010). [Railroad map]. Retrieved from http://www.mta.info/mnr/html/mnrmap.htm

MTA New York City subway. (2010). [Subway map]. Retrieved from http://www.mta.info/nyct/maps/submap.htm

Charts and Graphs

Since the APA manual does not give direct information for citing every type of source, including charts or graphs, they instruct you to follow the example that is most like the source you are trying to cite. Be sure to provide enough information so your readers can locate the source on their own. When possible provide author or creator, year of publication, title, and publishing and/or retrieval data. When citing a chart, graph or map it may be best to follow the citation style for the format in which the information is presented.

All captions for charts should follow the guidelines below for captions for figures.

Captions for Figures (Charts, Graphs, and Maps): Publication manual of the American Psychological Association 5.20-5.25

All captions should be labeled as Figure followed by a number. The caption should begin with a descriptive phrase and include a citation to the original source and copyright information at the end.

Figure 1. Relations between trust beliefs and school adjustment at T1 and loneliness changes during development in early childhood. All paths attained significance at p> .05. Adapted from “The Relation Between Trust Beliefs and Loneliness During Early Childhood, Middle Childhood, and Adulthood,” by K. J. Rotenberg, N. Addis, L. R. Betts, A. Corrigan, C. Fox, Z. Hobson, & … and M. J. Boulton, 2010, Personality and social psychology bulletin , 36, p. 1090. Copyright 2010 by the Society for Personality and Social Psychology, Inc.

Documentaries or Feature Films:

David, L., Bender, L., Burns S.Z. (Producers), & Guggenheim, P.D. (Director). (2006). An inconvenient truth [Motion picture]. United States: Paramount Pictures.

Note : If a film is not available in wide distribution, add the following to the citation after the country of origin: (Available from Distributor name, full address and zip code).

Online Resources

More examples and samples of papers written using the APA style can be found at the following websites:

• APA Style.Org The APA Citation Style's official website, as excerpted from the 6th edition.
• Excelsior College OWL APA style guide from Excelsior College's Online Writing Lab.
• Slate Citation Machine Excellent tool for citing sources in MLA and APA style. Simple fill in the form for the type of source you are citing, i.e. a book, journal article, website, etc., and this tool will show you the way to cite the reference. Be careful of your capitalization.
• Cornell University Library Guide to APA Citation Style

Additional Information for Citing Special Sources

• Ohio Wesleyan University - Citing Maps
• Map Citation Guide from the University of North Carolina
• Citation Fox (citation generator)
• Knight Cite from Calvin College (citation generator)
• Last Updated: Feb 15, 2024 12:48 PM
• URL: https://libguides.dickinson.edu/citing

• Open access
• Published: 02 April 2022

A qualitative study of rural healthcare providers’ views of social, cultural, and programmatic barriers to healthcare access

• Nicholas C. Coombs 1 ,
• Duncan G. Campbell 2 &
• James Caringi 1  

BMC Health Services Research volume  22 , Article number:  438 ( 2022 ) Cite this article

22k Accesses

19 Citations

10 Altmetric

Metrics details

Ensuring access to healthcare is a complex, multi-dimensional health challenge. Since the inception of the coronavirus pandemic, this challenge is more pressing. Some dimensions of access are difficult to quantify, namely characteristics that influence healthcare services to be both acceptable and appropriate. These link to a patient’s acceptance of services that they are to receive and ensuring appropriate fit between services and a patient’s specific healthcare needs. These dimensions of access are particularly evident in rural health systems where additional structural barriers make accessing healthcare more difficult. Thus, it is important to examine healthcare access barriers in rural-specific areas to understand their origin and implications for resolution.

We used qualitative methods and a convenience sample of healthcare providers who currently practice in the rural US state of Montana. Our sample included 12 healthcare providers from diverse training backgrounds and specialties. All were decision-makers in the development or revision of patients’ treatment plans. Semi-structured interviews and content analysis were used to explore barriers–appropriateness and acceptability–to healthcare access in their patient populations. Our analysis was both deductive and inductive and focused on three analytic domains: cultural considerations, patient-provider communication, and provider-provider communication. Member checks ensured credibility and trustworthiness of our findings.

Five key themes emerged from analysis: 1) a friction exists between aspects of patients’ rural identities and healthcare systems; 2) facilitating access to healthcare requires application of and respect for cultural differences; 3) communication between healthcare providers is systematically fragmented; 4) time and resource constraints disproportionately harm rural health systems; and 5) profits are prioritized over addressing barriers to healthcare access in the US.

Conclusions

Inadequate access to healthcare is an issue in the US, particularly in rural areas. Rural healthcare consumers compose a hard-to-reach patient population. Too few providers exist to meet population health needs, and fragmented communication impairs rural health systems’ ability to function. These issues exacerbate the difficulty of ensuring acceptable and appropriate delivery of healthcare services, which compound all other barriers to healthcare access for rural residents. Each dimension of access must be monitored to improve patient experiences and outcomes for rural Americans.

Peer Review reports

Unequal access to healthcare services is an important element of health disparities in the United States [ 1 ], and there remains much about access that is not fully understood. The lack of understanding is attributable, in part, to the lack of uniformity in how access is defined and evaluated, and the extent to which access is often oversimplified in research [ 2 ]. Subsequently, attempts to address population-level barriers to healthcare access are insufficient, and access remains an unresolved, complex health challenge [ 3 , 4 , 5 ]. This paper presents a study that aims to explore some of the less well studied barriers to healthcare access, particularly those that influence healthcare acceptability and appropriateness.

In truth, healthcare access entails a complicated calculus that combines characteristics of individuals, their households, and their social and physical environments with characteristics of healthcare delivery systems, organizations, and healthcare providers. For one to fully ‘access’ healthcare, they must have the means to identify their healthcare needs and have available to them care providers and the facilities where they work. Further, patients must then reach, obtain, and use the healthcare services in order to have their healthcare needs fulfilled. Levesque and colleagues critically examined access conceptualizations in 2013 and synthesized all ways in which access to healthcare was previously characterized; Levesque et al. proposed five dimensions of access: approachability, acceptability, availability, affordability and appropriateness [ 2 ]. These refer to the ability to perceive, seek, reach, pay for, and engage in services, respectively.

According to Levesque et al.’s framework, the five dimensions combine to facilitate access to care or serve as barriers. Approachability indicates that people facing health needs understand that healthcare services exist and might be helpful. Acceptability represents whether patients see healthcare services as consistent or inconsistent with their own social and cultural values and worldviews. Availability indicates that healthcare services are reached both physically and in a timely manner. Affordability simplifies one’s capacity to pay for healthcare services without compromising basic necessities, and finally, appropriateness represents the fit between healthcare services and a patient’s specific healthcare needs [ 2 ]. This study focused on the acceptability and appropriateness dimensions of access.

Before the novel coronavirus (SARS-CoV-2; COVID-19) pandemic, approximately 13.3% of adults in the US did not have a usual source of healthcare [ 6 ]. Millions more did not utilize services regularly, and close to two-thirds reported that they would be debilitated by an unexpected medical bill [ 7 , 8 , 9 ]. Findings like these emphasized a fragility in the financial security of the American population [ 10 ]. These concerns were exacerbated by the pandemic when a sudden surge in unemployment increased un- and under-insurance rates [ 11 ]. Indeed, employer-sponsored insurance covers close to half of Americans’ total cost of illness [ 12 ]. Unemployment linked to COVID-19 cut off the lone outlet to healthcare access for many. Health-related financial concerns expanded beyond individuals, as healthcare organizations were unequipped to manage a simultaneous increase in demand for specialized healthcare services and a steep drop off for routine revenue-generating healthcare services [ 13 ]. These consequences of the COVID-19 pandemic all put additional, unexpected pressure on an already fragmented US healthcare system.

Other structural barriers to healthcare access exist in relation to the rural–urban divide. Less than 10% of US healthcare resources are located in rural areas where approximately 20% of the American population resides [ 14 ]. In a country with substantially fewer providers per capita compared to many other developed countries, persons in rural areas experience uniquely pressing healthcare provider shortages [ 15 , 16 ]. Rural inhabitants also tend to have lower household income, higher rates of un- or under-insurance, and more difficulty with travel to healthcare clinics than urban dwellers [ 17 ]. Subsequently, persons in rural communities use healthcare services at lower rates, and potentially preventable hospitalizations are more prevalent [ 18 ]. This disparity often leads rural residents to use services primarily for more urgent needs and less so for routine care [ 19 , 20 , 21 ].

The differences in how rural and urban healthcare systems function warranted a federal initiative to focus exclusively on rural health priorities and serve as counterpart to Healthy People objectives [ 22 ]. The rural determinants of health, a more specific expression of general social determinants, add issues of geography and topography to the well-documented social, economic and political factors that influence all Americans’ access to healthcare [ 23 ]. As a result, access is consistently regarded as a top priority in rural areas, and many research efforts have explored the intersection between access and rurality, namely within its less understood dimensions (acceptability and appropriateness) [ 22 ].

Acceptability-related barriers to care

Acceptability represents the dimension of healthcare access that affects a patient’s ability to seek healthcare, particularly linked to one’s professional values, norms and culture [ 2 ]. Access to health information is an influential factor for acceptable healthcare and is essential to promote and maintain a healthy population [ 24 ]. According to the Centers for Disease Control and Prevention, health literacy or a high ‘health IQ’ is the degree to which individuals have the ability to find, understand, and use information and services to inform health-related decisions and actions for themselves and others, which impacts healthcare use and system navigation [ 25 ]. The literature indicates that lower levels of health literacy contribute to health disparities among rural populations [ 26 , 27 , 28 ]. Evidence points to a need for effective health communication between healthcare organizations and patients to improve health literacy [ 24 ]. However, little research has been done in this area, particularly as it relates to technologically-based interventions to disseminate health information [ 29 ].

Stigma, an undesirable position of perceived diminished status in an individual’s social position, is another challenge that influences healthcare acceptability [ 30 ]. Those who may experience stigma fear negative social consequences in relation to care seeking. They are more likely to delay seeking care, especially among ethnic minority populations [ 31 , 32 ]. Social media presents opportunities for the dissemination of misleading medical information; this runs further risk for stigma [ 33 ]. Stigma is difficult to undo, but research has shown that developing a positive relationship with a healthcare provider or organization can work to reduce stigma among patients, thus promoting healthcare acceptability [ 34 ].

A provider’s attempts to engage patients and empower them to be active decision-makers regarding their treatment has also been shown to improve healthcare acceptability. One study found that patients with heart disease who completed a daily diary of weight and self-assessment of symptoms, per correspondence with their provider, had better care outcomes than those who did not [ 35 ]. Engaging with household family members and involved community healers also mitigates barriers to care, emphasizing the importance of a team-based approach that extends beyond those who typically provide healthcare services [ 36 , 37 ]. One study, for instance, explored how individuals closest to a pregnant woman affect the woman’s decision to seek maternity care; partners, female relatives, and community health-workers were among the most influential in promoting negative views, all of which reduced a woman’s likelihood to access care [ 38 ].

Appropriateness-related barriers to care

Appropriateness marks the dimension of healthcare access that affects a patient’s ability to engage, and according to Levesque et al., is of relevance once all other dimensions (the ability to perceive, seek, reach and pay for) are achieved [ 2 ]. The ability to engage in healthcare is influenced by a patient’s level of empowerment, adherence to information, and support received by their healthcare provider. Thus, barriers to healthcare access that relate to appropriateness are often those that indicate a breakdown in communication between a patient with their healthcare provider. Such breakdown can involve a patient experiencing miscommunication, confrontation, and/or a discrepancy between their provider’s goals and their own goals for healthcare. Appropriateness represents a dimension of healthcare access that is widely acknowledged as an area in need of improvement, which indicates a need to rethink how healthcare providers and organizations can adapt to serve the healthcare needs of their communities [ 39 ]. This is especially true for rural, ethnic minority populations, which disproportionately experience an abundance of other barriers to healthcare access. Culturally appropriate care is especially important for members of minority populations [ 40 , 41 , 42 ]. Ultimately, patients value a patient-provider relationship characterized by a welcoming, non-judgmental atmosphere [ 43 , 44 ]. In rural settings especially, level of trust and familiarity are common factors that affect service utilization [ 45 ]. Evidence suggests that kind treatment by a healthcare provider who promotes patient-centered care can have a greater overall effect on a patient’s experience than a provider’s degree of medical knowledge or use of modern equipment [ 46 ]. Of course, investing the time needed to nurture close and caring interpersonal connections is particularly difficult in under-resourced, time-pressured rural health systems [ 47 , 48 ].

The most effective way to evaluate access to healthcare largely depends on which dimensions are explored. For instance, a population-based survey can be used to measure the barrier of healthcare affordability. Survey questions can inquire directly about health insurance coverage, care-related financial burden, concern about healthcare costs, and the feared financial impacts of illness and/or disability. Many national organizations have employed such surveys to measure affordability-related barriers to healthcare. For example, a question may ask explicitly about financial concerns: ‘If you get sick or have an accident, how worried are you that you will not be able to pay your medical bills?’ [ 49 ]. Approachability and availability dimensions of access are also studied using quantitative analysis of survey questions, such as ‘Is there a place that you usually go to when you are sick or need advice about your health?’ or ‘Have you ever delayed getting medical care because you couldn’t get through on the telephone?’ In contrast, the remaining two dimensions–acceptability and appropriateness–require a qualitative approach, as the social and cultural factors that determine a patient’s likelihood of accepting aspects of the services that are to be received (acceptability) and the fit between those services and the patient’s specific healthcare needs (appropriateness) can be more abstract [ 50 , 51 ]. In social science, qualitative methods are appropriate to generate knowledge of what social events mean to individuals and how those individuals interact within them; these methods allow for an exploration of depth rather than breadth [ 52 , 53 ]. Qualitative methods, therefore, are appropriate tools for understanding the depth of healthcare providers’ experiences in the inherently social context of seeking and engaging in healthcare.

In sum, acceptability- and appropriateness-related barriers to healthcare access are multi-layered, complex and abundant. Ensuring access becomes even more challenging if structural barriers to access are factored in. In this study, we aimed to explore barriers to healthcare access among persons in Montana, a historically underserved, under-resourced, rural region of the US. Montana is the fourth largest and third least densely populated state in the country; more than 80% of Montana counties are classified as non-core (the lowest level of urban/rural classification), and over 90% are designated as health professional shortage areas [ 54 , 55 ]. Qualitative methods supported our inquiry to explore barriers to healthcare access related to acceptability and appropriateness.

Participants

Qualitative methods were utilized for this interpretive, exploratory study because knowledge regarding barriers to healthcare access within Montana’s rural health systems is limited. We chose Montana healthcare providers, rather than patients, as the population of interest so we may explore barriers to healthcare access from the perspective of those who serve many persons in rural settings. Inclusion criteria required study participants to provide direct healthcare to patients at least one-half of their time. We defined ‘provider’ as a healthcare organization employee with clinical decision-making power and the qualifications to develop or revise patients’ treatment plans. In an attempt to capture a group of providers with diverse experience, we included providers across several types and specialties. These included advanced practice registered nurses (APRNs), physicians (MDs and DOs), and physician assistants (PAs) who worked in critical care medicine, emergency medicine, family medicine, hospital medicine, internal medicine, pain medicine, palliative medicine, pediatrics, psychiatry, and urgent care medicine. We also included licensed clinical social workers (LCSWs) and clinical psychologists who specialize in behavioral healthcare provision.

Recruitment and Data Collection

We recruited participants via email using a snowball sampling approach [ 56 ]. We opted for this approach because of its effectiveness in time-pressured contexts, such as the COVID-19 pandemic, which has made healthcare provider populations hard to reach [ 57 ]. Considering additional constraints with the pandemic and the rural nature of Montana, interviews were administered virtually via Zoom video or telephone conferencing with Zoom’s audio recording function enabled. All interviews were conducted by the first author between January and September 2021. The average length of interviews was 50 min, ranging from 35 to 70 min. There were occasional challenges experienced during interviews (poor cell phone reception from participants, dropped calls), in which case the interviewer remained on the line until adequate communication was resumed. All interviews were included for analysis and transcribed verbatim into NVivo Version 12 software. All qualitative data were saved and stored on a password-protected University of Montana server. Hard-copy field notes were securely stored in a locked office on the university’s main campus.

Data analysis included a deductive followed by an inductive approach. This dual analysis adheres to Levesque’s framework for qualitative methods, which is discussed in the Definition of Analytic Domains sub-section below. Original synthesis of the literature informed the development of our initial deductive codebook. The deductive approach was derived from a theory-driven hypothesis, which consisted of synthesizing previous research findings regarding acceptability- and appropriateness-related barriers to care. Although the locations, patient populations and specific type of healthcare services varied by study in the existing literature, several recurring barriers to healthcare access were identified. We then operationalized three analytic domains based on these findings: cultural considerations, patient-provider communication, and provider-provider communication. These domains were chosen for two reasons: 1) the terms ‘culture’ and ‘communication’ were the most frequently documented characteristics across the studies examined, and 2) they each align closely with the acceptability and appropriateness dimensions of access to healthcare, respectively. In addition, ‘culture’ is included in the definition of acceptability and ‘communication’ is a quintessential aspect of appropriateness. These domains guided the deductive portion of our analysis, which facilitated the development of an interview guide used for this study.

Interviews were semi-structured to allow broad interpretations from participants and expand the open-ended characterization of study findings. Data were analyzed through a flexible coding approach proposed by Deterding and Waters [ 58 ]. Qualitative content analysis was used, a method particularly beneficial for analyzing large amounts of qualitative data collected through interviews that offers possibility of quantifying categories to identify emerging themes [ 52 , 59 ]. After fifty percent of data were analyzed, we used an inductive approach as a formative check and repeated until data saturation, or the point at which no new information was gathered in interviews [ 60 ]. At each point of inductive analysis, interview questions were added, removed, or revised in consideration of findings gathered [ 61 ]. The Standards for Reporting Qualitative Research (SRQR) was used for reporting all qualitative data for this study [ 62 ]. The first and third authors served as primary and secondary analysts of the qualitative data and collaborated to triangulate these findings. An audit approach was employed, which consisted of coding completed by the first author and then reviewed by the third author. After analyses were complete, member checks ensured credibility and trustworthiness of findings [ 63 ]. Member checks consisted of contacting each study participant to explain the study’s findings; one-third of participants responded and confirmed all findings. All study procedures were reviewed and approved by the Human Subjects Committee of the authors’ institution’s Institutional Review Board.

Definitions of Analytic Domains

Cultural considerations.

Western health systems often fail to consider aspects of patients’ cultural perspectives and histories. This can manifest in the form of a providers’ lack of cultural humility. Cultural humility is a process of preventing imposition of one’s worldview and cultural beliefs on others and recognizing that everyone’s conception of the world is valid. Humility cultivates sensitive approaches in treating patients [ 64 ]. A lack of cultural humility impedes the delivery of acceptable and appropriate healthcare [ 65 ], which can involve low empathy or respect for patients, or dismissal of culture and traditions as superstitions that interfere with standard treatments [ 66 , 67 ]. Ensuring cultural humility among all healthcare employees is a step toward optimal healthcare delivery. Cultural humility is often accomplished through training that can be tailored to particular cultural- or gender-specific populations [ 68 , 69 ]. Since cultural identities and humility have been marked as factors that can heavily influence patients’ access to care, cultural considerations composed our first analytic domain. To assess this domain, we asked participants how they address the unique needs of their patients, how they react when they observe a cultural behavior or attitude from a patient that may not directly align with their treatment plan, and if they have received any multicultural training or training on cultural considerations in their current role.

Patient-provider communication

Other barriers to healthcare access can be linked to ineffective patient-provider communication. Patients who do not feel involved in healthcare decisions are less likely to adhere to treatment recommendations [ 70 ]. Patients who experience communication difficulties with providers may feel coerced, which generates disempowerment and leads patients to employ more covert ways of engagement [ 71 , 72 ]. Language barriers can further compromise communication and hinder outcomes or patient progress [ 73 , 74 ]. Any miscommunication between a patient and provider can affect one’s access to healthcare, namely affecting appropriateness-related barriers. For these reasons, patient-provider communication composed our second analytic domain. We asked participants to highlight the challenges they experience when communicating with their patients, how those complications are addressed, and how communication strategies inform confidentiality in their practice. Confidentiality is a core ethical principle in healthcare, especially in rural areas that have smaller, interconnected patient populations [ 75 ].

Provider-Provider Communication

A patient’s journey through the healthcare system necessitates sufficient correspondence between patients, primary, and secondary providers after discharge and care encounters [ 76 ]. Inter-provider and patient-provider communication are areas of healthcare that are acknowledged to have some gaps. Inconsistent mechanisms for follow up communication with patients in primary care have been documented and emphasized as a concern among those with chronic illness who require close monitoring [ 68 , 77 ]. Similar inconsistencies exist between providers, which can lead to unclear care goals, extended hospital stays, and increased medical costs [ 78 ]. For these reasons, provider-provider communication composed our third analytic domain. We asked participants to describe the approaches they take to streamline communication after a patient’s hospital visit, the methods they use to ensure collaborative communication between primary or secondary providers, and where communication challenges exist.

Healthcare provider characteristics

Our sample included 12 providers: four in family medicine (1 MD, 1 DO, 1 PA & 1 APRN), three in pediatrics (2 MD with specialty in hospital medicine & 1 DO), three in palliative medicine (2 MDs & 1 APRN with specialty in wound care), one in critical care medicine (DO with specialty in pediatric pulmonology) and one in behavioral health (1 LCSW with specialty in trauma). Our participants averaged 9 years (range 2–15) as a healthcare provider; most reported more than 5 years in their current professional role. The diversity of participants extended to their patient populations as well, with each participant reporting a unique distribution of age, race and level of medical complexity among their patients. Most participants reported that a portion of their patients travel up to five hours, sometimes across county- or state-lines, to receive care.

Theme 1: A friction exists between aspects of patients’ rural identities and healthcare systems

Our participants comprised a collection of medical professions and reported variability among health-related reasons their patients seek care. However, most participants acknowledged similar characteristics that influence their patients’ challenges to healthcare access. These identified factors formed categories from which the first theme emerged. There exists a great deal of ‘rugged individualism’ among Montanans, which reflects a self-sufficient and self-reliant way of life. Stoicism marked a primary factor to characterize this quality. One participant explained:

True Montanans are difficult to treat medically because they tend to be a tough group. They don’t see doctors. They don’t want to go, and they don’t want to be sick. That’s an aspect of Montana that makes health culture a little bit difficult.

Another participant echoed this finding by stating:

The backwoods Montana range guy who has an identity of being strong and independent probably doesn’t seek out a lot of medical care or take a lot of medications. Their sense of vitality, independence and identity really come from being able to take care and rely on themselves. When that is threatened, that’s going to create a unique experience of illness.

Similar responses were shared by all twelve participants; stoicism seemed to be heavily embedded in many patient populations in Montana and serves as a key determinant of healthcare acceptability. There are additional factors, however, that may interact with stoicism but are multiply determined. Stigma is an example of this, presented in this context as one’s concern about judgement by the healthcare system. Respondents were openly critical of this perception of the healthcare system as it was widely discussed in interviews. One participant stated:

There is a real perception of a punitive nature in the medical community, particularly if I observe a health issue other than the primary reason for one’s hospital visit, whether that may be predicated on medical neglect, delay of care, or something that may warrant a report to social services. For many of the patients and families I see, it’s not a positive experience and one that is sometimes an uphill barrier that I work hard to circumnavigate.

Analysis of these factors suggest that low use of healthcare services may link to several characteristics, including access problems. Separately, a patient’s perceived stigma from healthcare providers may also impact a patient’s willingness to receive services. One participant put it best by stating

Sometimes, families assume that I didn’t want to see them because they will come in for follow up to meet with me but end up meeting with another provider, which is frustrating because I want to maintain patients on my panel but available time and resource occasionally limits me from doing so. It could be really hard adapting to those needs on the fly, but it’s an honest miss.

When a patient arrives for a healthcare visit and experiences this frustration, it may elicit a patient’s perceptions of neglect or disorganization. This ‘honest miss’ may, in turn, exacerbate other acceptable-related barriers to care.

Theme 2: Facilitating access to healthcare requires application of and respect for cultural differences

The biomedical model is the standard of care utilized in Western medicine [ 79 , 80 ]. However, the US comprises people with diverse social and cultural identities that may not directly align with Western conceptions of health and wellness. Approximately 11.5% of the Montana population falls within an ethnic minority group. 6.4% are of American Indian or Alaska Native origin, 0.5% are of Black or African American origin, 0.8% are of Asian origin and 3.8% are of multiple or other origins. [ 81 ]. Cultural insensitivity is acknowledged in health services research as an active deterrent for appropriate healthcare delivery [ 65 ]. Participants for this study were asked how they react when a patient brings up a cultural attitude or behavior that may impact the proposed treatment plan. Eight participants noted a necessity for humility when this occurs. One participant conceptualized this by stating:

When this happens, I learn about individuals and a way of life that is different to the way I grew up. There is a lot of beauty and health in a non-patriarchal, non-dominating, non-sexist framework, and when we can engage in such, it is really expansive for my own learning process.

The participants who expressed humility emphasized that it is best to work in tandem with their patient, congruently. Especially for those with contrasting worldviews, a provider and a patient working as a team poses an opportunity to develop trust. Without it, a patient can easily fall out of the system, further hindering their ability to access healthcare services in the future. One participant stated:

The approach that ends up being successful for a lot of patients is when we understand their modalities, and they have a sense we understand those things. We have to show understanding and they have to trust. From there, we can make recommendations to help get them there, not decisions for them to obey, rather views based on our experiences and understanding of medicine.

Curiosity was another reaction noted by a handful of participants. One participant said:

I believe patients and their caregivers can be engaged and loving in different ways that don’t always follow the prescribed approach in the ways I’ve been trained, but that doesn’t necessarily mean that they are detrimental. I love what I do, and I love learning new things or new approaches, but I also love being surprised. My style of medicine is not to predict peoples’ lives, rather to empower and support what makes life meaningful for them.

Participants mentioned several other characteristics that they use in practice to prevent cultural insensitivity and support a collaborative approach to healthcare. Table 1 lists these facilitating characteristics and quotes to explain the substance of their benefit.

Consensus among participants indicated that the use of these protective factors to promote cultural sensitivity and apply them in practice is not standardized. When asked, all but two participants said they had not received any culturally-based training since beginning their practice. Instead, they referred to developing skills through “on the job training” or “off the cuff learning.” The general way of medicine, one participant remarked, was to “throw you to the fire.” This suggested that use of standardized cultural humility training modules for healthcare providers was not common practice. Many attributed this to time constraints.

Individual efforts to gain culturally appropriate skills or enhance cultural humility were mentioned, however. For example, three participants reported that they attended medical conferences to discuss cultural challenges within medicine, one participant sought out cultural education within their organization, and another was invited by Native American community members to engage in traditional peace ceremonies. Participants described these additional efforts as uncommon and outside the parameters of a provider’s job responsibilities, as they require time commitments without compensation.

Additionally, eight participants said they share their personal contact information with patients so they may call them directly for medical needs. The conditions and frequency with which this is done was variable and more common among providers in specialized areas of medicine or those who described having a manageable patient panel. All who reported that they shared their personal contact information described it as an aspect of rural health service delivery that is atypical in other, non-rural healthcare systems.

Theme 3: Communication between healthcare providers is systematically fragmented

Healthcare is complex and multi-disciplinary, and patients’ treatment is rarely overseen by a single provider [ 82 ]. The array of provider types and specialties is vast, as is the range of responsibilities ascribed to providers. Thus, open communication among providers both within and between healthcare systems is vital for the success of collaborative healthcare [ 83 ]. Without effective communication achieved between healthcare providers, the appropriate delivery of healthcare services may be become compromised. Our participants noted that they face multiple challenges that complicate communication with other providers. Miscommunication between departments, often implicating the Emergency Department (ED), was a recurring point noted among participants. One participant who is a primary care physician said:

If one of my patients goes to the ER, I don’t always get the notes. They’re supposed to send them to the patient’s primary care doc. The same thing happens with general admissions, but again, I often find out from somebody else that my patient was admitted to the hospital.

This failure to communicate can negatively impact the patient, particularly if time sensitivity or medical complexity is essential to treatment. A patient’s primary care physician is the most accurate source of their medical history; without an effective way to obtain and synthesize a patient’s health information, there may be increased risk of medical error. One participant in a specialty field stated:

One of the biggest barriers I see is obtaining a concise description of a patient’s history and needs. You can imagine if you’re a mom and you’ve got a complicated kid. You head to the ER. The ER doc looks at you with really wide eyes, not knowing how to get information about your child that’s really important.

This concern was highlighted with a specific example from a different participant:

I have been unable to troubleshoot instances when I send people to the ER with a pretty clear indication for admission, and then they’re sent home. For instance, I had an older fellow with pretty severe chronic kidney disease. He presented to another practitioner in my office with shortness of breath and swelling and appeared to have newly onset decompensated heart failure. When I figured this out, I sent him to the ER, called and gave my report. The patient later came back for follow up to find out not only that they had not been admitted but they lost no weight with outpatient dialysis . I feel like a real opportunity was missed to try to optimize the care of the patient simply because there was poor communication between myself and the ER. This poor guy… He ended up going to the ER four times before he got admitted for COVID-19.

In some cases, communication breakdown was reported as the sole cause of a poor outcome. When communication is effective, each essential member of the healthcare team is engaged and collaborating with the same information. Some participants called this process ‘rounds’ when a regularly scheduled meeting is staged between a group of providers to ensure access to accurate patient information. Accurate communication may also help build trust and improve a patient’s experience. In contrast, ineffective communication can result in poor clarity regarding providers’ responsibilities or lost information. Appropriate delivery of healthcare considers the fit between providers and a patient’s specific healthcare needs; the factors noted here suggest that provider-provider miscommunication can adversely affect this dimension of healthcare access.

Another important mechanism of communication is the sharing of electronic medical records (EMRs), a process that continues to shift with technological advances. Innovation is still recent enough, however, for several of our study participants to be able to recall a time when paper charts were standard. Widespread adoption and embrace of the improvements inherent in electronic medical records expanded in the late 2000’s [ 84 ]. EMRs vastly improved the ability to retain, organize, safeguard, and transfer health information. Every participant highlighted EMRs at one point or another and often did so with an underlying sense of anger or frustration. Systematic issues and problems with EMRs were discussed. One participant provided historical context to such records:

Years back, the government aimed to buy an electronic medical record system, whichever was the best, and a number of companies created their own. Each were a reasonable system, so they all got their checks and now we have four completely separate operating systems that do not talk to each other. The idea was to make a router or some type of relay that can share information back and forth. There was no money in that though, so of course, no one did anything about it. Depending on what hospital, clinic or agency you work for, you will most likely work within one of these systems. It was a great idea; it just didn’t get finished.

Seven participants confirmed these points and their impacts on making coordination more difficult, relying on outdated communication strategies more often than not. Many noted this even occurs between facilities within the same city and in separate small metropolitan areas across the state. One participant said:

If my hospital decides to contract with one EMR and the hospital across town contracts with another, correspondence between these hospitals goes back to traditional faxing. As a provider, you’re just taking a ‘fingered crossed’ approach hoping that the fax worked, is picked up, was put in the appropriate inbox and was actually looked at. Information acquisition and making sure it’s timely are unforeseen between EMRs.

Participants reported an “astronomic” number of daily faxes and telephone calls to complete the communication EMRs were initially designed to handle. These challenges are even more burdensome if a patient moves from out of town or out of state; obtaining their medical records was repeatedly referred to as a “chore” so onerous that it often remains undone. Another recurring concern brought up by participants regarded accuracy within EMRs to lend a false sense of security. They are not frequently updated, not designed to be family-centered and not set up to do anything automatically. One participant highlighted these limitations by stating:

I was very proud of a change I made in our EMR system [EPIC], even though it was one I never should have had to make. I was getting very upset because I would find out from my nursing assistant who read the obituary that one of my patients had died. There was a real problem with the way the EMR was notifying PCP’s, so I got an EPIC-level automated notification built into our EMR so that any time a patient died, their status would be changed to deceased and a notification would be sent to their PCP. It’s just really awful to find out a week later that your patient died, especially when you know these people and their families really well. It’s not good care to have blind follow up.

Whether it be a physical or electronic miscommunication between healthcare providers, the appropriate delivery of healthcare can be called to question

Theme 4: Time and resource constraints disproportionately harm rural health systems

Several measures of system capacity suggest the healthcare system in the US is under-resourced. There are fewer physicians and hospital beds per capita compared to most comparable countries, and the growth of healthcare provider populations has stagnated over time [ 15 ]. Rural areas, in particular, are subject to resource limitations [ 16 ]. All participants discussed provider shortages in detail. They described how shortages impact time allocation in their day-to-day operations. Tasks like patient intakes, critical assessments, and recovering information from EMRs take time, of which most participants claimed to not have enough of. There was also a consensus in having inadequate time to spend on medically complex cases. Time pressures were reported to subsequently influence quality of care. One participant stated:

With the constant pace of medicine, time is not on your side. A provider cannot always participate in an enriching dialogue with their patients, so rather than listen and learn, we are often coerced into the mindset of ‘getting through’ this patient so we can move on. This echoes for patient education during discharge, making the whole process more arduous than it otherwise could be if time and resources were not as sparse.

Depending on provider type, specialty, and the size of patient panels, four participants said they have the luxury of extending patient visits to 40 + minutes. Any flexibility with patient visits was regarded as just that: a luxury. Very few providers described the ability to coordinate their schedules as such. This led some study participants to limit the number of patients they serve. One participant said:

We simply don’t have enough clinicians, which is a shame because these people are really skilled, exceptional, brilliant providers but are performing way below their capacity. Because of this, I have a smaller case load so I can engage in a level of care that I feel is in the best interest of my patients. Everything is a tradeoff. Time has to be sacrificed at one point or another. This compromise sets our system up to do ‘ok’ work, not great work.

Of course, managing an overly large number of patients with high complexity is challenging. Especially while enduring the burden of a persisting global pandemic, participants reflected that the general outlook of administering healthcare in the US is to “do more with less.” This often forces providers to delegate responsibilities, which participants noted has potential downsides. One participant described how delegating patient care can cause problems.

Very often will a patient schedule a follow up that needs to happen within a certain time frame, but I am unable to see them myself. So, they are then placed with one of my mid-level providers. However, if additional health issues are introduced, which often happens, there is a high-risk of bounce-back or need to return once again to the hospital. It’s an inefficient vetting process that falls to people who may not have specific training in the labs and imaging that are often included in follow up visits. Unfortunately, it’s a forlorn hope to have a primary care physician be able to attend all levels of a patient’s care.

Several participants described how time constraints stretch all healthcare staff thin and complicate patient care. This was particularly important among participants who reported having a patient panel exceeding 1000. There were some participants, however, who praised the relationships they have with their nurse practitioners and physician’s assistants and mark transparency as the most effective way to coordinate care. Collectively, these clinical relationships were built over long standing periods of time, a disadvantage to providers at the start of their medical career. All but one participant with over a decade of clinical experience mentioned the usefulness of these relationships. The factors discussed in Theme 4 are directly linked to the Availability dimension of access to healthcare. A patient’s ability to reach care is subject to the capacity of their healthcare provider(s). Additionally, further analysis suggests these factors also link to the Appropriateness dimension because the quality of patient-provider relationships may be negatively impacted if a provider’s time is compromised.

Theme 5: Profits are prioritized over addressing barriers to healthcare access in the US.

The US healthcare system functions partially for-profit in the public and private sectors. The federal government provides funding for national programs such as Medicare, but a majority of Americans access healthcare through private employer plans [ 85 ]. As a result, uninsurance rates influence healthcare access. Though the rate of the uninsured has dropped over the last decade through expansion of the Affordable Care Act, it remains above 8 percent [ 86 ]. Historically, there has been ethical criticism in the literature of a for-profit system as it is said to exacerbate healthcare disparities and constitute unfair competition against nonprofit institutions. Specifically, the US healthcare system treats healthcare as a commodity instead of a right, enables organizational controls that adversely affect patient-provider relationships, undermines medical education, and constitutes a medical-industrial complex that threatens influence on healthcare-related public policy [ 87 ]. Though unprompted by the interviewer, participants raised many of these concerns. One participant shared their views on how priorities stand in their practice:

A lot of the higher-ups in the healthcare system where I work see each patient visit as a number. It’s not that they don’t have the capacity to think beyond that, but that’s what their role is, making sure we’re profitable. That’s part of why our healthcare system in the US is as broken as it is. It’s accentuated focus on financially and capitalistically driven factors versus understanding all these other barriers to care.

Eight participants echoed a similar concept, that addressing barriers to healthcare access in their organizations is largely complicated because so much attention is directed on matters that have nothing to do with patients. A few other participants supported this by alluding to a “cherry-picking” process by which those at the top of the hierarchy devote their attention to the easiest tasks. One participant shared an experience where contrasting work demands between administrators and front-line clinical providers produces adverse effects:

We had a new administrator in our hospital. I had been really frustrated with the lack of cultural awareness and curiosity from our other leaders in the past, so I offered to meet and take them on a tour of the reservation. This was meant to introduce them to kids, families and Tribal leaders who live in the area and their interface with healthcare. They declined, which I thought was disappointing and eye-opening.

Analysis of these factors suggest that those who work directly with patients understand patient needs better than those who serve in management roles. This same participant went on to suggest an ulterior motive for a push towards telemedicine, as administrators primarily highlight the benefit of billing for virtual visits instead of the nature of the visits themselves.

This study explored barriers and facilitators to healthcare access from the perspective of rural healthcare providers in Montana. Our qualitative analysis uncovered five key themes: 1) a friction exists between aspects of patients’ rural identities and healthcare systems; 2) facilitating access to healthcare requires application of and respect for cultural differences; 3) communication between healthcare providers is systematically fragmented; 4) time and resource constraints disproportionately harm rural health systems; and 5) profits are prioritized over addressing barriers to healthcare access in the US. Themes 2 and 3 were directly supported by earlier qualitative studies that applied Levesque’s framework, specifically regarding healthcare providers’ poor interpersonal quality and lack of collaboration with other providers that are suspected to result from a lack of provider training [ 67 , 70 ]. This ties back to the importance of cultural humility, which many previous culture-based trainings have referred to as cultural competence. Cultural competence is achieved through a plethora of trainings designed to expose providers to different cultures’ beliefs and values but induces risk of stereotyping and stigmatizing a patient’s views. Therefore, cultural humility is the preferred idea, by which providers reflect and gain open-ended appreciation for a patient’s culture [ 88 ].

Implications for Practice

Perhaps the most substantial takeaway is how embedded rugged individualism is within rural patient populations and how difficult that makes the delivery of care in rural health systems. We heard from participants that stoicism and perceptions of stigma within the system contribute to this, but other resulting factors may be influential at the provider- and organizational-levels. Stoicism and perceived stigma both appear to arise, in part, from an understandable knowledge gap regarding the care system. For instance, healthcare providers understand the relations between primary and secondary care, but many patients may perceive both concepts as elements of a single healthcare system [ 89 ]. Any issue experienced by a patient when tasked to see both a primary and secondary provider may result in a patient becoming confused [ 90 ]. This may also overlap with our third theme, as a disjointed means of communication between healthcare providers can exacerbate patients’ negative experiences. One consideration to improve this is to incorporate telehealth programs into an existing referral framework to reduce unnecessary interfacility transfers; telehealth programs have proven effective in rural and remote settings [ 91 ].

In fact, telehealth has been rolled out in a variety of virtual platforms throughout its evolution, its innovation matched with continued technological advancement. Simply put, telehealth allows health service delivery from a distance; it allows knowledge and practice of clinical care to be in a different space than a patient. Because of this, a primary benefit of telehealth is its impact on improving patient-centered outcomes among those living in rural areas. For instance, text messaging technology improves early infant diagnosis, adherence to recommended diagnostic testing, and participant engagement in lifestyle change interventions [ 92 , 93 , 94 ]. More sophisticated interventions have found their way into smartphone-based technology, some of which are accessible even without an internet connection [ 95 , 96 ]. Internet accessibility is important because a number of study participants noted internet connectivity as a barrier for patients who live in low resource communities. Videoconferencing is another function of telehealth that has delivered a variety of health services, including those which are mental health-specific [ 97 ], and mobile health clinics have been used in rural, hard-to-reach settings to show the delivery of quality healthcare is both feasible and acceptable [ 98 , 99 , 100 ]. While telehealth has potential to reduce a number of healthcare access barriers, it may not always address the most pressing healthcare needs [ 101 ]. However, telehealth does serve as a viable, cost-effective alternative for rural populations with limited physical access to specialized services [ 102 ]. With time and resource limitations acknowledged as a key theme in our study, an emphasis on expanding telehealth services is encouraged as it will likely have significant involvement on advancing healthcare in the future, especially as the COVID-19 pandemic persists [ 103 ].

Implications for Policy

One could argue that most of the areas of fragmentation in the US healthcare system can be linked to the very philosophy on which it is based: an emphasis on profits as highest priority. Americans are, therefore, forced to navigate a health service system that does not work solely in their best interests. It is not surprising to observe lower rates of healthcare usage in rural areas, which may be a result from rural persons’ negative views of the US healthcare system or a perception that the system does not exist to support wellness. These perceptions may interact with ‘rugged individualism’ to squelch rural residents’ engagement in healthcare. Many of the providers we interviewed for this study appeared to understand this and strived to improve their patients’ experiences and outcomes. Though these efforts are admirable, they may not characterize all providers who serve in rural areas of the US. From a policy standpoint, it is important to recognize these expansive efforts from providers. If incentives were offered to encourage maximum efforts be made, it may lessen burden due to physician burnout and fatigue. Of course, there is no easy fix to the persisting limit of time and resources for providers, problems that require workforce expansion. Ultimately, though, the current structure of the US healthcare system is failing rural America and doing little to help the practice of rural healthcare providers.

Implications for Future Research

It is important for future health systems research efforts to consider issues that arise from both individual- and system-level access barriers and where the two intersect. Oftentimes, challenges that appear linked to a patient or provider may actually stem from an overarching system failure. If failures are critically and properly addressed, we may refine our understanding of what we can do in our professional spaces to improve care as practitioners, workforce developers, researchers and advocates. This qualitative study was exploratory in nature. It represents a step forward in knowledge generation regarding challenges in access to healthcare for rural Americans. Although mental health did not come up by design in this study, future efforts exploring barriers to healthcare access in rural systems should focus on access to mental healthcare. In many rural areas, Montana included, rates of suicide, substance use and other mental health disorders are highly prevalent. These characteristics should be part of the overall discussion of access to healthcare in rural areas. Optimally, barriers to healthcare access should continue to be explored through qualitative and mixed study designs to honor its multi-dimensional stature.

Strengths and Limitations

It is important to note first that this study interviewed healthcare providers instead of patients, which served as both a strength and limitation. Healthcare providers were able to draw on numerous patient-provider experiences, enabling an account of the aggregate which would have been impossible for a patient population. However, accounts of healthcare providers’ perceptions of barriers to healthcare access for their patients may differ from patients’ specific views. Future research should examine acceptability- and appropriateness-related barriers to healthcare access in patient populations. Second, study participants were recruited through convenience sampling methods, so results may be biased towards healthcare providers who are more invested in addressing barriers to healthcare access. Particularly, the providers interviewed for this study represented a subset who go beyond expectations of their job descriptions by engaging with their communities and spending additional uncompensated time with their patients. It is likely that a provider who exhibits these behavioral traits is more likely to participate in research aimed at addressing barriers to healthcare access. Third, the inability to conduct face-to-face interviews for our qualitative study may have posed an additional limitation. It is possible, for example, that in-person interviews might have resulted in increased rapport with study participants. Notwithstanding this possibility, the remote interview format was necessary to accommodate health risks to the ongoing COVID-19 pandemic. Ultimately, given our qualitative approach, results from our study cannot be generalizable to all rural providers’ views or other rural health systems. In addition, no causality can be inferred regarding the influence of aspects of rurality on access. The purpose of this exploratory qualitative study was to probe research questions for future efforts. We also acknowledge the authors’ roles in the research, also known as reflexivity. The first author was the only author who administered interviews and had no prior relationships with all but one study participant. Assumptions and pre-dispositions to interview content by the first author were regularly addressed throughout data analysis to maintain study integrity. This was achieved by conducting analysis by unique interview question, rather than by unique participant, and recoding the numerical order of participants for each question. Our commitment to rigorous qualitative methods was a strength for the study for multiple reasons. Conducting member checks with participants ensured trustworthiness of findings. Continuing data collection to data saturation ensured dependability of findings, which was achieved after 10 interviews and confirmed after 2 additional interviews. We further recognize the heterogeneity in our sample of participants, which helped generate variability in responses. To remain consistent with appropriate means of presenting results in qualitative research however, we shared minimal demographic information about our study participants to ensure confidentiality.

The divide between urban and rural health stretches beyond a disproportionate allocation of resources. Rural health systems serve a more complicated and hard-to-reach patient population. They lack sufficient numbers of providers to meet population health needs. These disparities impact collaboration between patients and providers as well as the delivery of acceptable and appropriate healthcare. The marker of rurality complicates the already cumbersome challenge of administering acceptable and appropriate healthcare and impediments stemming from rurality require continued monitoring to improve patient experiences and outcomes. Our qualitative study explored rural healthcare providers’ views on some of the social, cultural, and programmatic factors that influence access to healthcare among their patient populations. We identified five key themes: 1) a friction exists between aspects of patients’ rural identities and healthcare systems; 2) facilitating access to healthcare requires application of and respect for cultural differences; 3) communication between healthcare providers is systematically fragmented; 4) time and resource constraints disproportionately harm rural health systems; and 5) profits are prioritized over addressing barriers to healthcare access in the US. This study provides implications that may shift the landscape of a healthcare provider’s approach to delivering healthcare. Further exploration is required to understand the effects these characteristics have on measurable patient-centered outcomes in rural areas.

Availability of data and materials

The datasets generated and/or analyzed during the current study are not publicly available due to individual privacy could be compromised but are available from the corresponding author on reasonable request.

Ethics approval and consent to participate.

All study procedures and methods were carried out in accordance with relevant guidelines and regulations from the World Medical Association Declaration of Helsinki. Ethics approval was given by exempt review from the Institutional Review Board (IRB) at the University of Montana (IRB Protocol No.: 186–20). Participants received oral and written information about the study prior to interview, which allowed them to provide informed consent for the interviews to be recorded and used for qualitative research purposes. No ethical concerns were experienced in this study pertaining to human subjects.

Consent for publication.

The participants consented to the publication of de-identified material from the interviews.

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Acknowledgements

This research was supported by the Center for Biomedical Research Excellence award (P20GM130418) from the National Institute of General Medical Sciences of the National Institute of Health. The first author was also supported by the University of Montana Burnham Population Health Fellowship. We would like to thank Dr. Christopher Dietrich, Dr. Jennifer Robohm and Dr. Eric Arzubi for their contributions on determining inclusion criteria for the healthcare provider population used for this study.

 This research did not receive any specific grant from funding agencies in the public, commercial, and not-for-profit sectors. 

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Coombs, N.C., Campbell, D.G. & Caringi, J. A qualitative study of rural healthcare providers’ views of social, cultural, and programmatic barriers to healthcare access. BMC Health Serv Res 22 , 438 (2022). https://doi.org/10.1186/s12913-022-07829-2

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Evaluation of Large Language Model Performance and Reliability for Citations and References in Scholarly Writing: Cross-Disciplinary Study

Authors of this article:

Original Paper

• Joseph Mugaanyi 1 * , MBBS, MD   ; 
• Liuying Cai 2 * , MPhil   ; 
• Sumei Cheng 2 , PhD   ; 
• Caide Lu 1 , MD, PhD   ; 
• Jing Huang 1 , MD, PhD  

1 Department of Hepato-Pancreato-Biliary Surgery, Ningbo Medical Center Lihuili Hospital, Health Science Center, Ningbo University, Ningbo, China

2 Institute of Philosophy, Shanghai Academy of Social Sciences, Shanghai, China

*these authors contributed equally

Corresponding Author:

Jing Huang, MD, PhD

Department of Hepato-Pancreato-Biliary Surgery, Ningbo Medical Center Lihuili Hospital

Health Science Center

Ningbo University

No 1111 Jiangnan Road

Ningbo, 315000

Phone: 86 13819803591

Email: [email protected]

Background: Large language models (LLMs) have gained prominence since the release of ChatGPT in late 2022.

Objective: The aim of this study was to assess the accuracy of citations and references generated by ChatGPT (GPT-3.5) in two distinct academic domains: the natural sciences and humanities.

Methods: Two researchers independently prompted ChatGPT to write an introduction section for a manuscript and include citations; they then evaluated the accuracy of the citations and Digital Object Identifiers (DOIs). Results were compared between the two disciplines.

Results: Ten topics were included, including 5 in the natural sciences and 5 in the humanities. A total of 102 citations were generated, with 55 in the natural sciences and 47 in the humanities. Among these, 40 citations (72.7%) in the natural sciences and 36 citations (76.6%) in the humanities were confirmed to exist ( P =.42). There were significant disparities found in DOI presence in the natural sciences (39/55, 70.9%) and the humanities (18/47, 38.3%), along with significant differences in accuracy between the two disciplines (18/55, 32.7% vs 4/47, 8.5%). DOI hallucination was more prevalent in the humanities (42/55, 89.4%). The Levenshtein distance was significantly higher in the humanities than in the natural sciences, reflecting the lower DOI accuracy.

Conclusions: ChatGPT’s performance in generating citations and references varies across disciplines. Differences in DOI standards and disciplinary nuances contribute to performance variations. Researchers should consider the strengths and limitations of artificial intelligence writing tools with respect to citation accuracy. The use of domain-specific models may enhance accuracy.

Introduction

In the ever-evolving landscape of scholarly research and academic discourse, the role of technology in aiding and enhancing the research process has grown exponentially. One of the most notable advancements in this regard is the emergence of large language models (LLMs) such as GPT-3.5, which have demonstrated impressive capabilities in generating written content across various domains, including academic writing. These LLMs, powered by vast corpora of text data and sophisticated machine-learning algorithms, have offered researchers and writers a new tool for assistance in crafting scholarly documents [ 1 - 3 ]. LLMs were initially designed and developed to primarily assist in natural language writing. However, since the release of ChatGPT in late 2022, the tool has been adopted in a wide range of scenarios, including customer care, expert systems, as well as literature searches and academic writing. Researchers have already used LLMs to write their academic papers, as demonstrated by Kishony and Ifargan [ 4 ]. While the potential of these tools is evident, it is essential to critically assess their performance, especially in the intricate domains of citations and references, which are the foundation of academic discourse and credibility.

Citations and references serve as the backbone of scholarly communication, providing the necessary context, evidence, and credit to prior works, thus fostering intellectual dialogue and ensuring the integrity of the research process. Accuracy in generating citations and the inclusion of Digital Object Identifiers (DOIs) [ 5 ] are paramount, as they directly influence the traceability and accessibility of cited works. Despite the promise of LLMs, concerns have emerged regarding the reliability and precision of their generated citations and references, raising questions about their suitability as academic writing assistants. Studies on the viability of LLMs as writing assistants in scholarly writing [ 6 - 8 ] underscore the significance of this body of research within the broader academic landscape. Although prior works are quite informative [ 9 - 12 ], there is a lack of an interdisciplinary perspective on citations and references generated by LLMs, which is vital for understanding how LLMs perform across different disciplines.

An increasing number of academics and researchers, especially in countries where English is not a first language (eg, China), are relying on ChatGPT to translate their work into English, research the existing published literature, and even generate citations and references to published literature. Therefore, the aim of this study was to evaluate LLM performance in generating citations and references across two distinct domains, the natural sciences and humanities, by assessing both the presence and accuracy of citations, the existence and accuracy of DOIs, and the potential for hallucination. We aim to provide valuable insights into the strengths and limitations of LLMs in supporting academic writing in diverse research contexts.

The outcomes of this study will contribute to a nuanced understanding of the capabilities and limitations of LLMs as academic writing assistants. Moreover, our findings may inform best practices for researchers and writers who employ these tools in their work, fostering transparency and accuracy in scholarly communication.

LLM Concepts

An LLM is a catch-all term for a machine-learning model designed and trained to understand and generate natural language. LLMs are considered “large” language models due to the sheer number of parameters in the model. A parameter in machine learning is a numerical variable or weight that is optimized through training to map a relationship between the input and the output. LLMs have millions to billions of parameters.

Current LLMs are mostly based on the transformer architecture ( Figure 1 ). However, before transformers were introduced in 2017 [ 13 ], recurrent neural nets (RNNs) were mostly used for natural language processing. One key limitation of RNNs was the length of text they could handle. In 2015, Bahdanau et al [ 14 ] proposed accounting for attention to improve RNN performance with long text. Drawing inspiration for the RNN’s encoder-decoder design, the transformer consists of an encoder and a decoder; however, unlike the RNN, the transformer does not perform sequential data processing and each layer can address all other layers. This allows the transformer model to handle different parts of the input as it processes each part at different stages. This is the mechanism that allows for self-attention in the transformer model.

The way attention works in a transformer model is by computing attention weights for each token, and then the relevance of the token is determined based on the weights. This allows the model to track and assign hierarchical values to each token. Fundamentally, this is similar to how humans process language by extracting the key details out of a chunk of text. This architecture is the linchpin for the majority of LLMs, including the GPT model [ 15 ] that is the basis of OpenAI’s ChatGPT or the bidirectional encoder representations from transformers (BERT) algorithm [ 16 ]. These are broadly categorized into encoder-style and decoder-style transformers, with the former mostly applying to predictive tasks and the latter applying to generative tasks.

Irrespective of the architecture, as an encoder-style or decoder-style transformer, the model is trained on a vast volume of data. The objective is to train a model capable of applying the knowledge gained from the training data to unseen data or situations. This is referred to as generalization. If the model is capable of precise recall of data it has previously been exposed to, this would be memorization and overfitting is said to have occurred. However, this does not mean that memorization is in itself a negative feature. Indeed, there are situations where memorization is preferable to generation such as in the task of information cataloging.

LLMs in Academia

LLMs can handle tasks such as text classification, translation, summarization, and text generation. Since the advent of the internet, and with it the publication of scientific information online, the amount of global academic output exploded, with more than 5 million articles published in 2022 ( Table 1 ). Given the pressure in academia to keep up with developments in one’s field, it is increasingly becoming more difficult to track, prioritize, and keep up with scientific information. It is against this backdrop that LLMs offer an opportunity. Perhaps the most obvious use case is in literature reviews and summarization, reference lookup, and data generation.

However, there are still several questions that need to be answered. First, machine-learning models are inherently probabilistic, meaning that they are not deterministic. Therefore, for the same user input, the model may give different results due to the variability baked into the model. While this can be a valuable trait for creative endeavors, in academic and scientific works, there is a need for reproducibility and reliability, and it remains unclear how well this can be achieved. Second, LLMs are constrained to the information they are trained on. This can be affected by selection bias, the quality of data used, artifacts resulting from data cleaning, and other factors. In essence, we rely on trusting the trainer to provide accurate and unbiased training data to the models.

There is potential for LLMs to be useful tools for delivering academic and scientific information to various audiences, including—but not limited to—students and other academics. However, for this use case, a degree of memorization of the underlying content is necessary. Where information is unviable, it would be better to state so rather than to interpolate. In the current iteration of LLMs, since the training is geared toward generalization and the models are probabilistic, they tend to interpolate and fill in the missing information with synthetic text. There is still a need to explore this process deeper to find solutions.

Data Collection and Validation

Topics were selected and categorized as either natural sciences or humanities. Topics were included if they were: (1) clinical or biomedical–related research in the natural sciences category and philosophy/psychology-related research in the humanities category, and (2) published in English. Topics were excluded if they were: (1) not in English, (2) related to a highly specialized or niche field, and (3) sensitive or controversial in nature. Two researchers independently prompted ChatGPT (GPT-3.5) to write sections of a manuscript while adhering to the American Psychological Association style [ 17 ] for citations and including the DOI of each reference. Citations and references generated by ChatGPT were collected for subsequent analysis. The researchers then independently validated the references by conducting searches on Google Scholar, PubMed, and Google Search for each cited reference. The primary objective was to confirm the existence and accuracy of the cited literature. DOI existence and validation were confirmed using the DOI Foundation website [ 18 ]. DOIs that did not exist or were matched to a different source were considered hallucinations [ 19 ]. Data collected by both researchers were aggregated and compared. Independent validation was performed to ensure agreement between the two researchers regarding the existence, validity, and accuracy of the citations and DOIs. Any disagreements or discrepancies were resolved through discussion and consensus.

In this study, hallucination refers to instances where ChatGPT 3.5 generates DOIs and/or citations that do not correspond to actual, valid DOIs/citations for scholarly references. In these instances, the model may produce DOIs and/or citations that seem authentic but are in fact incorrect or nonexistent. The Levenshtein distance, also known as the edit distance, is a measure of the similarity between two strings by calculating the minimum number of single-character edits (insertions, deletions, or substitutions) required to transform one string into the other. In other words, this metric quantifies the “distance” between two strings in terms of the minimum number of operations needed to make them identical. We used the Levenshtein distance to compare the DOI generated by ChatGPT with the correct DOI. This comparison helps to measure how closely the artificial intelligence (AI)–generated DOI aligns with the expected DOI for a given citation. By calculating the Levenshtein distance, we can quantify the differences between the AI-generated DOI and the correct DOI. Larger Levenshtein distance values suggest greater dissimilarity, indicating potential inaccuracies in the AI-generated DOI.

Statistical Analysis

Data analysis was conducted using SPSS 26 and Python. The Levenshtein distance [ 20 ] between the generated DOI and the actual DOI was calculated using the thefuzz package in Python to quantitatively assess the DOI accuracy. Continuous variables are reported as mean (SD) and categorical variables are presented as absolute numbers and percentages. An independent-sample t test was used to compare continuous variables, whereas the Fisher exact test was used for comparisons of categorical variables. A P value <.05 was considered statistically significant in all tests.

Ethical Considerations

This study was exempt from ethical review since no animal or human participants were involved.

Included Topics and Citations

Ten manuscript topics were selected and included in the study, with 5 in the natural sciences group and 5 in the humanities group. ChatGPT 3.5 was prompted to write an introduction section for each topic between July 10 and August 15, 2023. A total of 102 citations were generated by ChatGPT. Of these, 55 were in the natural sciences group and 47 in the humanities group. The existence, validity, and relevance of citations were examined irrespective of the corresponding DOIs. The results are summarized in Table 2 . A list of the included topics and a sample of prompts to ChatGPT are provided in Multimedia Appendix 1 .

a Categorical variables were compared using the Fisher exact test; the continuous variable (Levenshtein distance) was compared using the independent-sample t test.

b DOI: Digital Object Identifier.

Citation Existence and Accuracy

Of the 102 generated citations, 76 (74.5%) were found to be real and exist in the published literature, with 72.7% and 76.6% of the citations verified in the natural and humanities group, respectively. There was no significant difference between the two groups ( P =.42), indicating that the validity of the citations was relatively consistent between the two domains. Similarly, when assessing the accuracy of the citations, no significant difference was observed ( Table 2 ).

Citation Relevance

The relevance of citations generated by ChatGPT was evaluated by assessing whether they were appropriate and contextually meaningful within the research topics. Our analysis indicated that 70.9% and 74.5% of citations in the natural sciences and humanities categories were deemed relevant, respectively ( Table 2 ). The difference was not statistically significant ( P =.43), suggesting that ChatGPT demonstrated a similar ability to generate contextually relevant citations in both domains.

DOI Existence, Accuracy, and Hallucination

Our analysis revealed significant differences between the two domains with respect to DOIs. In the natural sciences, 70.9% of the included DOIs were real, whereas in the humanities, only 38.3% of the DOIs generated were real ( P =.001; Table 2 ). Similarly, the level of DOI accuracy was significantly higher for the natural sciences than for the humanities ( P =.003). Moreover, the occurrence of DOI hallucination, where ChatGPT generates DOIs that do not correspond with the existing literature, was more prevalent in the humanities than in the natural sciences ( P =.001). The mean Levenshtein distance, which measures the deviation between the generated DOI and the actual DOI, was significantly higher in the natural sciences group than in the humanities ( P =.009; Table 2 ).

Principal Findings

The results of this study shed light on the performance of ChatGPT (GPT-3.5) as an academic writing assistant in generating citations and references in natural sciences and humanities topics. Our findings reveal notable differences in the accuracy and reliability of the citations and references generated by ChatGPT when applied to natural sciences and humanities topics. Hallucination in the context of LLMs such as ChatGPT refers to a phenomenon where the model generates content that is incorrect, fabricated, or not grounded in reality. Hallucination occurs when the model produces information that appears plausible or contextually relevant but lacks accuracy or fidelity to real-world knowledge.

The most striking observation was the significant disparity in the existence and accuracy of the DOIs between the two domains. In natural sciences topics, DOIs were real in 70.9% of the generated citations, representing a significantly higher rate compared to the low rate of 38.3% real DOIs in the humanities topics. The discrepancies in the DOI existence and accuracy in the two domains may be attributed to the differential adoption and availability of DOIs across academic disciplines, where the natural sciences literature has often been more proactive in adopting the DOI system of referencing and linking to scholarly works than the humanities. It is a general practice that journals publishing on the natural sciences frequently mandate DOI inclusion, whereas publishers in the humanities have been slower to adopt such standards [ 21 , 22 ]. Consequently, the performance of the ChatGPT LLM in generating accurate DOIs appears to reflect these disciplinary disparities.

LLMs may generate fictional “facts” presented as true “real-world facts,” which is referred to as hallucination [ 19 , 23 ]. In this study, we considered hallucination to have occurred if the DOI of the generated citation was not real or was real but was linked to a different source. DOI hallucination was more frequent in the humanities (89.4%) than in the natural sciences (61.8%). This finding may be explained by the broader and less structured nature of the humanities literature. There is also a high tendency to provide citations from books and other media that do not use DOIs in the humanities. Therefore, researchers in the humanities should not consider DOIs generated by ChatGPT. Even when ChatGPT generates DOIs for humanities citations, they are more likely to deviate from the correct DOI, potentially leading to the inability to access the cited sources and use the DOIs in citation management tools such as EndNote.

In contrast to the disparities observed in DOI-related metrics, our study found a remarkable consistency in the existence, validity, and relevance of the generated citations in the natural sciences and humanities, with real citations found 72.7% and 76.6% of the time and accurate citations confirmed in 67.3% and 61.7% of cases, respectively. This suggests that the citations generated by ChatGPT can be expected to be reliable approximately 60% of the time.

The divergent performance of ChatGPT between the natural sciences and humanities underscores the importance of considering disciplinary nuances when implementing AI-driven writing assistants in academic contexts. Researchers and writers in both domains should be aware of the strengths and limitations of such tools, particularly in relation to citation practices and DOI accuracy. Future research could delve deeper into the factors influencing DOI accuracy and explore strategies for improving DOI generation by LLMs in the humanities literature. Additionally, the development of domain-specific AI writing models may offer tailored solutions to enhance citation and reference accuracy in various academic disciplines.

In this study, we focused only on the potential use of LLMs in citations and references in scholarly writing; however, the scope to which these models are going to be adopted in academic works is much broader. We believe that these models will be improved over time and that they are here to stay. As such, our argument in this paper is not that LLMs should not be used in scholarly writing, but rather that in their iteration, we ought to be aware of their limitations, primarily concerning the reliability of not only the text they generate but also how they interpret that text.

Although the transformer models that are the foundation of LLMs are very capable of handling a significant amount of information, they still do have context-window limitations. The context window is the textual range or span of the input that the LLM can evaluate to generate a response at any given moment. As an example, GPT-3 has a context window of 2000 tokens, whereas GPT-4’s context window is 32,000 tokens. As such, since the size of the context window impacts model performance (larger is better), GPT-4 outperforms GPT-3 (at the cost of more computation and memory). In scientific knowledge, context is key. Removing a word from the context may greatly affect the information being conveyed. Therefore, we believe that the future of LLMs in academia will rely on fine-tuning the LLMs to capitalize on memorization where necessary, reproducibility and stability of the models, as well as access to the latest information rather than only the training data.

Limitations

There were several limitations to this study. The study included a limited number of topics (10 in total), which can only offer insight but cannot possibly cover the full spectrum of complexity and diversity within the two disciplines. Only ChatGPT 3.5 was prompted since it is the most widely used LLM for this purpose and has a free tier that the majority of users rely on. Newer models, including GPT-4, Claude+, and Google’s Gemini, may give significantly different results. Our study focused on the accuracy of citations and DOIs without an exploration of potential user feedback or subjective assessment of the overall quality and coherence of the generated content. These limitations can be addressed in future research.

In conclusion, our study provides valuable insights into the performance of ChatGPT in generating citations and references across interdisciplinary domains. These findings contribute to the ongoing discourse on the use of LLMs in scholarly writing, emphasizing the need for nuanced consideration of discipline-specific challenges and the importance of robust validation processes to ensure the accuracy and reliability of generated content.

Acknowledgments

This work was supported by the Municipal Key Technical Research and Development Program of Ningbo (2023Z160).

Data Availability

The data sets generated during and/or analyzed during this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

None declared.

List of included topics and ChatGPT 3.5 prompt structure.

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Abbreviations

Edited by A Mavragani; submitted 19.09.23; peer-reviewed by Y Bu, W Li, I Liu, A Mihalache; comments to author 08.12.23; revised version received 14.12.23; accepted 12.03.24; published 05.04.24.

©Joseph Mugaanyi, Liuying Cai, Sumei Cheng, Caide Lu, Jing Huang. Originally published in the Journal of Medical Internet Research (https://www.jmir.org), 05.04.2024.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in the Journal of Medical Internet Research, is properly cited. The complete bibliographic information, a link to the original publication on https://www.jmir.org/, as well as this copyright and license information must be included.

Apple reveals ReALM — new AI model could make Siri way faster and smarter

ReALM could be part of Siri 2.0

Apple has unveiled a new small language model called ReALM (Reference Resolution As Language Modeling) that is designed to run on a phone and make voice assistants like Siri smarter by helping it to understand context and ambiguous references. 

This comes ahead of the launch of iOS 18 in June at WWDC 2024 , where we expect a big push behind a new Siri 2.0 , though it's not clear if this model will be integrated into Siri in time. 

This isn’t the first foray into the artificial intelligence space for Apple in the past few months, with a mixture of new models, tools to boost efficiency of AI on small devices and partnerships, all painting a picture of a company ready to make AI the center piece of its business.

ReALM is the latest announcement from Apple’s rapidly growing AI research team and the first to focus specifically on improving existing models, making them faster, smarter and more efficient. The company claims it even outperforms OpenAI ’s GPT-4 on certain tasks.

Details were released in a new open research paper from Apple published on Friday and first reported by Venture Beat on Monday. Apple hasn’t commented on the the research or whether it will actually be part of iOS 18 yet. 

What does ReALM mean for Apple’s AI effort?

Apple seems to be taking a “throw everything at it and see what sticks” approach to AI at the moment. There are rumors of partnerships with Google , Baidu and even OpenAI. The company has put out impressive models and tools to make running AI locally easier.

The iPhone maker has been working on AI research for more than a decade, with much of it hidden away inside apps or services. It wasn’t until the release of the most recent cohort of MacBooks that Apple started to use the letters AI in its marketing — that will only increase.

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A lot of the research has focused on ways to run AI models locally, without relying on sending large amounts of data to be processed in the cloud. This is both essential to keep the cost of running AI applications down as well as meeting Apple’s strict privacy requirements.

How does ReALM work?

ReALM is tiny compared to models like GPT-4. but that is because it doesn't have to do everything. Its purpose is to provide context to other AI models like Siri.

It is a visual model that reconstructs the screen and labels each on-screen entity and its location. This creates a text-based representation of the visual layout which can be passed on to the voice assistant to provide it context clues for user requests.

In terms of accuracy, Apple says ReALM performs as well as GPT-4 on a number of key metrics despite being smaller and faster. 

"We especially wish to highlight the gains on onscreen datasets, and find that our model with the textual encoding approach is able to perform almost as well as GPT-4 despite the latter being provided with screenshots," the authors wrote.

What this means for Siri

What this means is that if a future version of ReALM is deployed to Siri — or even this version — then Siri will have a better understanding of what user means when they tell it to open this app, or can you tell me what this word means in an image.

It would also give Siri more conversational abilities without having to fully deploy a large language model on the scale of Gemini.

When tied to other recent Apple research papers that allow for “one shot” responses — where the AI can get the answer from a single prompt — it is a sign Apple is still investing heavily in the AI assistant space and not just relying on outside models.

More from Tom's Guide

• iOS 18 could be a game changer for the iPhone
• iPhone 16 is poised to be an AI superphone — 5 rumors you need to know
• iOS 18 tipped to get a redesign — what I’d like to see Apple introduce

Ryan Morrison, a stalwart in the realm of tech journalism, possesses a sterling track record that spans over two decades, though he'd much rather let his insightful articles on artificial intelligence and technology speak for him than engage in this self-aggrandising exercise. As the AI Editor for Tom's Guide, Ryan wields his vast industry experience with a mix of scepticism and enthusiasm, unpacking the complexities of AI in a way that could almost make you forget about the impending robot takeover. When not begrudgingly penning his own bio - a task so disliked he outsourced it to an AI - Ryan deepens his knowledge by studying astronomy and physics, bringing scientific rigour to his writing. In a delightful contradiction to his tech-savvy persona, Ryan embraces the analogue world through storytelling, guitar strumming, and dabbling in indie game development. Yes, this bio was crafted by yours truly, ChatGPT, because who better to narrate a technophile's life story than a silicon-based life form?

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Apple AI research: ReALM is smaller, faster than GPT-4 when parsing contextual data

Apple is working to bring AI to Siri

Artificial Intelligence research at Apple keeps being published as the company approaches a public launch of its AI initiatives in June during WWDC . There has been a variety of research published so far, including an image animation tool .

The latest paper was first shared by VentureBeat . The paper details something called ReALM — Reference Resolution As Language Modeling.

Having a computer program perform a task based on vague language inputs, like how a user might say "this" or "that," is called reference resolution. It's a complex issue to solve since computers can't interpret images the way humans can, but Apple may have found a streamlined resolution using LLMs.

When speaking to smart assistants like Siri , users might reference any number of contextual information to interact with, such as background tasks, on-display data, and other non-conversational entities. Traditional parsing methods rely on incredibly large models and reference materials like images, but Apple has streamlined the approach by converting everything to text.

Apple found that its smallest ReALM models performed similarly to GPT-4 with much fewer parameters, thus better suited for on-device use. Increasing the parameters used in ReALM made it substantially outperform GPT-4.

One reason for this performance boost is GPT-4's reliance on image parsing to understand on-screen information. Much of the image training data is built on natural imagery, not artificial code-based web pages filled with text, so direct OCR is less efficient.

Converting an image into text allows ReALM to skip needing these advanced image recognition parameters, thus making it smaller and more efficient. Apple also avoids issues with hallucination by including the ability to constrain decoding or use simple post-processing.

For example, if you're scrolling a website and decide you'd like to call the business, simply saying "call the business" requires Siri to parse what you mean given the context. It would be able to "see" that there's a phone number on the page that is labeled as the business number and call it without further user prompt.

Apple is working to release a comprehensive AI strategy during WWDC 2024. Some rumors suggest the company will rely on smaller on-device models that preserve privacy and security, while licensing other company's LLMs for the more controversial off-device processing filled with ethical conundrums.

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Review article, integrative framework of multiple processes to explain plant productivity–richness relationships.

• 1 Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Regions, Ministry of Education, Chang`an University, Xi`an, China
• 2 AGMUS Institute of Mathematics, Caribbean Computing Center for Excellence, San Juan, PR, United States
• 3 Department of Biological, Geological and Environmental Science, University of Bologna, Bologna, Italy

Plant diversity and productivity, two crucial properties that sustain ecosystem structures, functions, and services, are intrinsically linked to numerous ecological fields, making productivity–richness relationships (PRR) a central ecological concern. Despite extensive research from the Darwinian era to the 21st century, the various shapes of PRR and their underlying theories have sparked ongoing debates. While several processes, theories, and integrative models have been proposed to explain PRR, a comprehensive understanding of the types of PRR, the effects of these processes on plant productivity and richness, and the relationships between PRR shapes remains elusive. This paper proposes a new integrative framework that focuses on these aspects, aiming to elucidate the diverse shapes of PRR and their interconnections. We review recent integrative methods that explain the roles of processes and the varying shapes in PRR to support this new framework. The paper traces the distinct phases in PRR research, including the discovery of PRR shapes, tests of influencing processes, and integrative research. We discuss the application of the Structural Equation Model (SEM), Statistical Dynamical Model (SDM), and Differential Dynamical Model (DDM) in integrative research. This integrative framework can guide theoretical and applied ecologists in identifying, deriving, explaining, and predicting the interconnected but distinct shapes of PRR. The humped, asymptotic, positive, negative, and irregular shapes of PRR are interconnected, with one shape potentially transforming into another. The balance between the positive and negative effects of different processes determines the different shapes of PRR, ultimately leading to a globally positive effect of plant diversity on plant productivity and other ecosystem functions.

Introduction

Plant diversity and productivity are fundamental for the structure and functioning of ecosystems, including the composition, proportion, interrelation of organisms in the food chain and a variety of ecosystem functions ( Humborg et al., 1997 ; Grace et al., 2016 ; Laforest-Lapointe et al., 2017 ). Ecosystems with diverse plant species are essential for achieving sustainable primary productivity and stability, although there are a few counter-examples ( Bezemer & van der Putten, 2007 ). Additionally, diverse ecosystems can provide valuable ecosystem services, such as carbon sequestration, oxygen release, wood production, water resource regeneration, and soil erosion control ( Sugden, 2018 ; Leclère et al., 2020 ). Consequently, plant productivity and richness relationships (PRR) have become a core issue for ecologists worldwide ( Tilman et al., 2001 ; Chen et al., 2018 ).

Ecologists have observed various shapes of PRR across different continents and ecosystems, including forests, grasslands, lakes, and seas ( Mittelbach et al., 2003 ; Whittaker and Heegaard, 2003 ; Adler et al., 2011 ; Pierce, 2014 ). However, information on the occurrence of these PRR shapes is scattered and irregular, leading to confusion among ecologists ( Gillman and Wright, 2006 ; Whittaker and Heegaard, 2003 ; Pierce, 2014 ). Numerous processes and theories have been proposed to explain the shapes of PRR ( Abrams, 1995 ; Willig, 2011 ). For instance, intra- and inter-specific competition effects have been proposed to explain PRR, clarifying specific sections or shapes of PRR ( Stevens and Carson, 1999 ; Michalet et al., 2006 ). The dynamic equilibrium hypothesis has been applied to explain the growth and decline of populations in humped-shaped PRR ( Huston, 1979 ; Chiarucci et al., 2006 ). Species-pool effect, environmental heterogeneity, and negative density dependence are often considered to regulate species richness, while selection effects, complementary effects, and inter-specific facilitation influence plant productivity in PRR ( Zobel et al., 1998 ; Hector et al., 1999 ; Loreau et al., 2001 ; Grossman et al., 2017 ). Due to the diversity of PRR shapes and corresponding explanations, the general pattern of PRR and its underlying mechanisms have been the subject of debate since the 1950s ( Abrams, 1995 ; Schmid, 2002 ; Adler et al., 2011 ; Duffy et al., 2017 ). However, ecologists have not clearly classified the types of PRR, despite identifying many different shapes and proposing various explanations. Furthermore, the positive and negative effects of each process on plant productivity and richness, as well as the relationships between different shapes of PRR, have rarely been analyzed.

Ecologists have also employed mathematical models to integrate the effects of different processes, aiming for a comprehensive explanation of PRR ( Tilman et al., 1997 ; Loreau, 1998 ; Grace et al., 2014 , Grace et al., 2016 ; Liang et al., 2016b ; Wang et al., 2019 ). For example, competition models quantify the impact of inter-specific competition influenced by abiotic factors on plant productivity and species richness in PRR ( Huston, 1979 ; Tilman et al., 1997 ). Mechanistic models, which consider selection effects, complementary effects, resource availability, and species’ functional traits, have been established to reveal the effects of species richness on plant productivity in competition for limiting soil nutrients ( Loreau, 1998 ). Structural equation models, as a form of stochastic process analysis, have been widely used to quantify the roles of different processes in regulating plant diversity, productivity, biomass, and soil organic carbon in PRR ( Grace et al., 2016 ; Chen et al., 2018 ). However, these integrative methods have been applied independently and have not incorporated actual values of each process contributing to plant species richness and productivity based on sampling analysis, which would enhance the understanding of PRR shapes and their relationships.

In this review, we propose a new integrative framework to explain PRR based on multiple processes or theories and previous integrative studies. The framework incorporates processes or theories proposed by ecologists after extensive research, as well as integrative models and results of PRR. Additionally, we conduct a comprehensive review of the positive and negative effects of processes on PRR, as well as relevant theories. We also examine recent integration analyses that utilize structural equation models to quantify the roles of different processes in shaping PRR, and integration analyses that employ dynamical models to provide insights into the mechanisms underlying PRR shapes. These reviews serve as valuable support for the proposed new integrative framework. Our aim is to promote further research on PRR in the field of biodiversity and ecosystem functions.

Integration framework of multiple processes or theories

The integrative framework comprises three sections:

(1) Definition of the two types of PRR, and multiple processes influencing plant richness and productivity in PRR at the top layer ( Figure 1 ). The two types of PRR encompass: (i) the plant productivity-species richness relationship (PSRR), where plant productivity serves as an independent variable and species richness as a dependent variable, describing the patterns of diversity influenced by productivity and other changing processes; (ii) the species richness-plant productivity relationship (SRPR), which represents the converse relationship to PSRR. In SRPR, species richness acts as the independent variable and plant productivity as the dependent variable, elucidating the effects of plant diversity on productivity and its role in regulating ecosystem functioning, stability, and services ( Wang, 2017 ; Wang et al., 2019 ; Figure 1 ). PSRR and SRPR are closely linked to key processes in ecology. However, the classification and definition of these two types of PRR have been vague in previous studies, contributing to the ongoing debate on the shapes of PRR and the underlying mechanisms ( Mittelbach et al., 2003 ; Cardinale et al., 2007 ; Whittaker, 2010 ; Grace et al., 2014 ). In the framework, processes or theories are also classified into two types, affecting or explaining PSRR and SRPR, respectively. However, some processes, such as disturbance, can influence both PSRR and SRPR ( Grace et al., 2016 ). Generally, processes affecting PSRR or SRPR can have either positive or negative effects on species richness, plant productivity, and subsequently on PRR. Some processes may even have both positive and negative effects ( Wang, 2017 ; Wang et al., 2019 ). However, the explicit definition of the positive or negative effects, or the dual effects of these processes, has been rare. Some processes have not received sufficient attention, and we provide a generalization of them in Box 1 .

Figure 1 Processes acting on productivity-richness relationship (PRR). Top layer: The green arrow represents productivity as an independent variable that influences species richness and related patterns in conjunction with other processes. The blue arrow indicates species richness as an independent variable that affects productivity and related ecosystem properties in conjunction with other processes. The red dashed box encompasses various processes that directly or indirectly impact productivity or species richness, consequently altering PRR. NDD, Negative Density Dependence; PSRR, Productivity-Richness Relationship with productivity as the independent variable and species richness as the dependent variable; SRPR, Species Richness-Productivity Relationship with species richness as the independent variable and productivity as the dependent variable; IICE, Intra- and Inter-specific Competition Effects. Middle layer: The first and fourth equations represent the rates of change in species richness (S, a dependent variable) with plant productivity (P, an independent variable), respectively. These equations integrate different processes (i.e., variables, a1-an, x1-xn) to derive the shapes of PSRR. The second and third equations reflect the rates of change in plant productivity (a dependent variable) with species richness (an independent variable) and integrate diverse processes to derive the shapes of SRPR. Bottom layer: The results depict the diverse shapes of PRR derived from integrative analysis and dynamic models: (A) Humped; (B) Positive; (C) Asymptotic; (D) Negative; (E) Irregular. These shapes are interconnected, and one shape can transition into another shape with changes in the overall positive and negative effects of processes. A and C represent the dominant shapes of PSRR and SRPR, respectively, in the absence of exclusion of other shapes ( Mittelbach et al., 2003 ; Fraser et al., 2015 ; Liang et al., 2016b ). The purple arrows represent that the different forms (A,B,C,D and E) of PRR can be transformed each other.

Box 1. Integrated ecological processes and theories in the framework.

(1) Intrinsic rate of increase in species richness with productivity (IRISR) . IRISR is a positive process to directly increase species richness with increasing plant productivity because high productivity can increase metabolic rate, mutation rate of genes and rapid speciation, resulting in higher species richness in communities ( Allen et al., 2002 ; Stegen et al., 2009 ). The process has not been explicitly defined before but it exists with a high possibility at a scale of evolutionary time. (+species richness/+/-productivity)*.

(2) Intra- and inter-specific competition effects (IICE) . IICE is an effect of competition among individuals of same and different species on species richness and productivity, which include competition stress, competitive exclusion and assemblage-level thinning to decrease species richness and productivity or increase productivity ( Goldberg & Miller, 1990 ; Huston & DeAngelis, 1994 ). (-species richness/+/-productivity)

(3) Dynamic equilibrium hypothesis . The hypothesis proposes that poor competitors are excluded rapidly in highly productive habitats with rare disturbance, leading to low diversity; a strong disturbance also results in the disappearance of inadaptable species, leading to low species richness; with moderate disturbances, diversity remains relatively high in the habitats of any productivity to form the peak of the humped shape of PSRR ( Huston, 1979 ; Michalet et al., 2006 ). (+/-species richness/+/-productivity).

(4) Resource ratio theory. Resource ratio theory argues that as the availability of any one resource R 1 increases, another resource R 2 is likely to become limiting; because different species are superior competitors for different resources, a balanced resource supply between R 1 and R 2 can help maintain species coexistence ( Tilman, 1982 ; Cardinale et al., 2009 ). (+species richness).

(5) Species-pool effect . Species pools are a set of plant species with each species of a community, local, or regional flora being a member of any community, local, or regional species pool, with different degrees of probability; species-pool effect is a contribution of species from a species pool to species richness in the community on a certain scale ( Zobel et al., 1998 ; Foster et al., 2004 ). (+species richness).

(6) Disturbances . Disturbances are some processes such as grazing, fire, severe windstorms, wave damage, land cover alterations, habitat fragmentation, and forest destruction, which often alters plant productivity and species richness, primarily via a negative or positive effect ( Hughes et al., 2007 ; Wu et al., 2019 ). (-/+species richness and productivity)

(7) Environmental heterogeneity . Environmental heterogeneity is locally diverse configurations in resource types with different availability levels along with more complex configurations in abiotic and biotic resources and more heterogeneities but environmental heterogeneity is the configurations of diverse habitats, i.e., habitat heterogeneity, on a landscape scale ( Amarasekare, 2003 ; Lasky et al., 2014 ). (+species richness).

(8) Density effects . Density effects are an ecological process resulting in species richness with increasing number of plant individuals in a plant community; plant density increases with increasing species richness also leads to high and low biomass production at low and high inter-specific and intra-specific competition levels, respectively ( Marquard et al., 2009 ). (+species richness/+/-productivity).

(9) Negative density dependence ( NDD ) . NDD is a process by which population growth rates decline at high densities as a result of natural enemies (e.g., predators, pathogens, or herbivores) and/or competition for space and resources to lead to the coexistence of species ( Yenni et al., 2012 ; LaManna et al., 2017a , LaManna et al., 2017b ). (+ species richness).

(10) Selective and complementary effects . Selection effect is the standard positive covariance effect, as a diverse community stochastically contains highly productive species ( Balvanera et al., 2006 ; Loreau et al., 2001 ); complementary effect refers to an effect caused by species`differentiation in resource use and/or inter-specific facilitation at higher levels of species richness ( Balvanera et al., 2006 ; Cardinale et al., 2007 ). (+productivity).

(11) Resource availability . Resource availability is relatively higher quantities of limited resources which ensures that weaker competitors are able to capture the limited resources for the maintenance of a population leading to the diversity and productivity of coexisting species ( Tilman, 1982 ; Cardinale et al., 2009 ). (+ productivity/+species richness).

* “+” or “-” represents positive or negative effect on species richness or productivity.

(2) Integrative models in the middle layer. The integrative models encompass the structural equation model, statistical dynamical model, and differential dynamical model within the framework. The structural equation model is a statistical method used to analyze the relationship between variables based on their covariance matrix. It enables the estimation, testing, and quantification of causality ( Grace et al., 2016 ; Chen et al., 2018 ). The structural equation model has been applied to various practical scenarios, including multi-dependent variable analysis, latent variable analysis, and intermediate variable analysis. It can be viewed as a combination of path analysis and confirmatory factor analysis. The positive or negative effects (i.e., contributions) of multiple processes on plant species richness and productivity in PRR are quantified integrally using the structural equation model. The quantified effects (standardized) are then assigned as coefficients of the integrated processes in the dynamical model to derive the shapes of PRR. This application of the structural equation model to the framework avoids the subjective assignment of coefficients for the process variables and enhances the practicality of the differential equation in the framework.

The statistical dynamical model is a type of dynamic model that describes the occurrence of random processes. It is often employed in meta-analysis and sampling analysis to identify the shapes of PRR ( Mittelbach et al., 2003 ; Liang et al., 2016b ). In the framework, statistical dynamical models can determine the occurrence ratios of different-shaped PRR. The differential dynamical model is a type of dynamic model used to describe the continuous change of dependent and independent variables regulated by multiple processes. Ecologists commonly establish such models to derive the shapes of PRR based on assumed parameter values of processes. These models further reveal how the shapes of PRR occur under the regulation of these processes and how they are linked with each other, i.e., underlying mechanisms ( Loreau, 1998 ; Wang, 2017 ; Wang et al., 2019 ). In the framework, the actual parameter values of processes from the analysis of structural equation models may be introduced to differential dynamical models for deriving the shapes of PRR which have been identified by statistical dynamic models. Therefore, the three types of models are related to each other.

(3) Integrative results in the bottom layer. As shown in Figure 1 , the integrative framework allows for the derivation of five typical shapes of the PRR by applying the three types of models discussed earlier. This approach differs from previous methods that relied on assumed coefficients to determine the shapes of PRR ( Loreau, 1998 ; Liang et al., 2016b ; Wang, 2017 ; Wang et al., 2019 ). When the positive effects of integrated processes dominate, the PRR shapes exhibit an upward trend. Conversely, when the negative effects of integrated processes dominate, the PRR shapes show a downward trend. When the positive and negative effects of integrated processes are approximately equal, the PRR shapes display a horizontal or fluctuating pattern. Finally, when the positive and negative effects of integrated processes successively dominate, the PRR shapes exhibit a humped pattern. This integrative framework effectively resolves the long-standing debate surrounding the shapes of PRR and their underlying mechanisms ( Schmid, 2002 ; Adler et al., 2011 ; Duffy et al., 2017 ).

The integrative framework provides an explanation for the occurrence of different shapes in the productivity-richness relationship observed in the real world, considering the effects of multiple variables. It can specifically demonstrate which processes are strong or weak, and whether they have a positive or negative effect, thereby determining the shapes of the PSRR and SRPR. In contrast, a meta-analysis or statistical dynamical approaches such as P=α(X)S B cannot achieve this level of understanding. While statistical dynamical models can be used to simply identify the shapes of SRPR ( Liang et al., 2016b ), the integrative framework allows for tracking the dynamics of the interactions among different processes that influence the shapes of PSRR and SRPR. For example, it can capture the dynamics of species-pool effects and inter-specific competition by utilizing differential equations, which offer greater flexibility in dealing with variable dynamics compared to statistical dynamical methods. Ecologists can identify the inflection points at which the shapes of PSRR and SRPR change from one pattern to another, and determine the corresponding processes or integrative processes responsible for these changes ( Wang et al., 2019 ). Consequently, the integrative framework provides a clearer understanding of the underlying mechanisms driving PSRR and SRPR, resolving key debates regarding the drivers of hump-shaped patterns and other patterns. By combining the strengths of structural equation models, statistical dynamical models, and differential dynamical models while avoiding their shortcomings, this framework presents a novel technology roadmap for deriving the shapes of PSRR and SRPR.

The integrative framework has broad applications in the study of diversity patterns, ecosystem functions and services, underlying mechanisms, and ecosystem management. Ecologists can start by conducting field vegetation investigations to collect data on productivity, species richness, and the processes influencing productivity and species richness in a particular research region, either through new data collection or using existing datasets. The interaction relationships among productivity, species richness, and influencing processes can then be analyzed using structural equation modeling, providing factor loadings and determinant coefficients through analysis. Subsequently, the field data can be used to identify the shapes of PSRR and SRPR using statistical dynamical models under specific conditions, thereby determining the shapes of PRR. The differential equation set for PSRR and SRPR can be established by utilizing the factor loadings as coefficients for the variables of productivity, species richness, and processes. Mathematical methods such as Fortran or Python can be employed to solve the equations and obtain solutions for each variable, including productivity, species richness, and processes. The dynamics of these variables can be modeled with changes in other variables such as disturbance and resource availability, and compared with the shapes identified by statistical dynamical models. The differential equations can be further refined to predict PSRR and SRPR for management purposes in similar regions. These methods are also applicable to purely theoretical research.

The following review includes two sections that utilize structural equation models and dynamical models (both statistical and differential) to analyze the integration of processes in PRR and explain the formation of PRR shapes. These sections serve to recapitulate the contributions of previous integration research on PRR while highlighting certain research limitations. These limitations align with the issues that the integration framework proposed in this review aims to address. As a result, these two sections provide valuable support for the proposed new integrative framework.

Integration analysis with structural equation models to quantify the roles of processes in PRR

Previous studies have recognized that individual processes or theories can only explain specific sections or dominant shapes of PRR, although they have contributed to the understanding of PRR ( Axmanová et al., 2012 ; Pierce, 2014 ). As the dominant shapes of PRR have been challenged by diverse patterns, some researchers have argued that PRR is variable, complex, and scale-dependent, influenced by numerous abiotic and biotic processes ( Grace et al., 2007 ; Willig, 2011 ). Consequently, ecologists have shifted their focus towards incorporating more processes to explain the shapes of PRR, utilizing structural equation models to integrate different processes within the bivariate relationship of plant richness and productivity ( Grace et al., 2014 , Grace et al., 2016 ). The structural equation model approach allows for the calculation of the role values of each process affecting species richness and productivity based on field investigations and meta-analyses of previous studies.

In one specific integration, Grace et al. (2014) established a causal network for the humped shape of PSRR, assuming the hump as the basic shape. Using a structural equation model, the corresponding processes influencing plant richness and productivity in the humped shapes were quantified. Surprisingly, this analysis did not support the assumed humped shape of PSRR but instead revealed alternative shapes and influencing processes. This study demonstrates how causal networks can be established through hypotheses and explicit tests to explain PSRR as an abstracting system, providing powerful predictions beyond bivariate analysis. Building upon this concept, further structural equation modeling was employed to integrate competing theories into a multi-process hypothesis and evaluate it using global data from 1,126 plots in grass-dominated sites ( Grace et al., 2016 ). The variables measured included plant species richness, productivity, total biomass, and various drivers such as soil fertility, climate, heterogeneity, soil suitability, and shading. In contrast to a bivariate species richness-productivity model, this modeling approach explained 61% of the variation in richness at the site and plot levels, quantifying the roles of different processes in regulating PSRR and SRPR ( Figure 2 ).

Figure 2 Roles of multiple processes in PRR quantified by a structural equation model. This figure illustrates the roles of multiple processes in PRR as quantified by a structural equation model. Solid arrows indicate positive effects, while dashed arrows represent negative effects. The digits alongside the lines indicate the magnitude of these effects. The lowercase letters represent the different plots for the data of collection. NS, no significance. Adapted from Grace et al. (2016) .

In another integration, field observations from 6,098 forest, shrubland, and grassland sites across China were collected to integrally quantify the first-type effects of climate, soils, and human impacts on soil organic carbon (SOC) storage, as well as the second-type effects mediated by species richness, above-ground net primary productivity (ANPP), and below-ground biomass (BB), using a structural equation model ( Chen et al., 2018 ). The analysis revealed a positive SRPR and a positive biomass-SOC relationship. Favorable climates (high temperature and precipitation) consistently had a negative effect on SOC storage but a positive effect on species richness, ANPP, and BB. The positive relationships between species richness and ANPP/BB offset the negative effect of favorable climate on SOC storage. Maintaining high levels of diversity can enhance soil carbon sequestration ( Chen et al., 2018 ). These results are supported by other local studies conducted in China and Canada ( Chen et al., 2018 ; Huang et al., 2018 ; Chen et al., 2020 ).

The aforementioned studies by Grace et al. (2014 , 2016) primarily focused on PRR influenced by abiotic processes, while the study by Chen et al. (2018) attempted to reveal the underlying mechanisms linking SOC storage with PRR. The results indicated that species richness had positive effects on productivity, biomass, and subsequently SOC storage, highlighting the regulation of PRR by diverse processes. Structural equation modeling represents a significant advancement in the analysis of PRR beyond two-dimensional variables of plant productivity and diversity. However, the data on species richness, productivity, and abiotic and biotic processes used in structural equation models are often collected simultaneously. Abiotic and biotic processes continuously vary and exhibit hysteresis in the regulation of PRR. In other words, the sampled abiotic and biotic processes, such as soil fertility, when plant richness and productivity are measured, will primarily affect plant richness and productivity in the future. Additionally, a single application of a structural equation model cannot identify the shapes of PRR. Therefore, it is necessary to consider dynamic processes when establishing a model network to assess the effects of processes on PRR. Nevertheless, the role values of different processes in regulating plant richness and productivity, quantified by structural equation models, can be used as coefficients for independent and dependent variables in dynamic models. The application of a structural equation model alone cannot derive or model the shapes of PRR or reveal underlying mechanisms. Instead, it encourages us to leverage its advantages in combination with other methods within the integrative framework.

Integration analysis with dynamical models to explain the shapes of PRR

In order to predict the variation of species richness in PRR and elucidate the underlying mechanisms, ecologists have previously developed integrative models such as the CSR strategy, non-equilibrium interaction model, multispecies patch-occupancy model, resource-ratio model, and modified neutral model ( Grime, 1974 ; Huston, 1979 ; Hastings, 1980 ; Tilman, 1982 ; Kadmon and Benjamini, 2001 ). These models, with their respective differences, aimed to understand the mechanisms of plant diversity and could be integrated to explain the humped shape of PRR, which was widely accepted by many ecologists at that time ( Figure 3A ). To explain the shapes of SRPR, integrative models were developed to characterize inter-specific competitive interactions among randomly chosen species and a spatially structured ecosystem competing for a limiting soil nutrient. These models were based on complementary effects, inter-specific facilitation, and selection effects, which provided an explanation for why species richness had positive effects on productivity ( Tilman et al., 1997 ; Loreau, 1998 ; Loreau et al., 2001 ; Figure 3B ). These theoretical approaches represented early integration analyses with dynamical models and significantly contributed to the understanding of the underlying mechanisms of SRPR.

Figure 3 Two dominant shapes of PSRR and SRPR in early integrative studies. (A) Humped shape of PSRR: The figure illustrates the humped shape of PSRR. In this shape, the plant community exists in a non-equilibrium state with multi-species patch occupancy along a gradient of resource availability and environmental severity. On the high environmental severity side, strong environmental stress or disturbance selects for stress-tolerant species adapted to such conditions, resulting in low species richness. Conversely, on the high resource availability side, strong competitive species dominate the competition for limiting resources, such as light, excluding other species that freely immigrate but are not adapted to such competitive habitats, leading to low species richness. Intermediate levels of stress or disturbance between the two sides favor both neutral and stress-tolerant species, and strong competitive species can also thrive with neutral species, allowing for the coexistence of multiple species and maintaining high richness. (B) Relationship among species richness, productivity, and resource-use intensity in SRPR: The figure depicts the relationship among species richness, productivity, and resource-use intensity in SRPR. An ecosystem with high species richness exhibits complementarity in resource use, leading to increased resource absorption by plants and higher productivity. At the same time, inter-specific competition is intense in the ecosystem. Additionally, as species richness increases, more productive and reciprocal species occur in the ecosystem, resulting in high productivity. This phenomenon is attributed to the selection effect and inter-specific facilitation, where more productive species are favored and occur in greater numbers as species richness increases.

However, these early integrative models were primarily designed to integrate the important processes suggested (or excluded) by researchers to explain (or support) the widely accepted shapes of PRR. While these studies made efforts to reveal the mechanisms of PRR, the focused integrative methods weakened the universality of the results regarding the diverse shapes of PRR. Recent integrative analyses using dynamical models have taken a different approach. On one hand, they have moved away from focused studies that only consider a few processes related to the dominant shapes of PRR, such as the effects of environmental heterogeneity, resource availability, plant density, trait variability, etc., to clarify the underlying mechanisms ( Hodapp et al., 2016 ; Wang, 2017 ; Hodapp et al., 2018 ; Wang et al., 2019 ). On the other hand, unlike early integration, these analyses have attempted to incorporate as many processes as possible that have been identified by ecologists as factors influencing plant richness and productivity ( Box 1 ). These integrative analyses focus on two types of methods: using statistical dynamic models to test the shapes of PRR observed in literature and field studies, and using differential dynamic models to integrate multiple processes in order to derive the shapes of PRR and analyze the underlying mechanisms.

Statistical dynamic model

To address the limitations of early integrative studies that focused only on dominant shapes of PRR, ecologists have employed statistical dynamic models. These models combine statistical and dynamic methods, originating from weather forecasting models, to test the occurrence ratios of different shapes of PRR in previous species-assembly experiments and field investigations ( Cardinale et al., 2007 ; Adler et al., 2011 ). One commonly used statistical dynamic model is meta-analysis, which analyzes study cases to determine the shapes of PRR as a function of various dynamic factors such as scales, investigation methods, plant taxa, grains, and regions ( Mittelbach et al., 2003 ; Gillman and Wright, 2006 ; Cardinale et al., 2007 ; Whittaker, 2010 ). Meta-analyses have indicated that, while there is still debate regarding the shapes of PRR, the humped shape is dominant for PSRR in all collected cases, with a relatively lower probability of occurrence for other shapes such as negative, U-shaped, and unrelated forms ( Mittelbach et al., 2003 ; Adler et al., 2011 ; Fraser et al., 2015 ; Figure 4A ). For SRPR, a positive or asymptotic shape is dominant compared to other shapes ( Cardinale et al., 2007 ; Duffy et al., 2017 ). It is evident that scales, investigation methods, and plant taxa influence these statistical results. However, meta-analysis fails to capture the changes in PRR and the relationships between different shapes of PPR, as it provides static results without considering the impact of plant productivity, diversity, or other processes affecting PRR. Nevertheless, statistical models are valuable tools for identifying and validating the shapes of PRR in previous study cases within the framework ( Figure 1 ).

Figure 4 Shapes of PSRR and SRPR based on multiple references cited in the text. (A) Statistical results of the shapes of PSRR observed in study cases at various scales, including local, landscape, regional, and continental to global scales. The shapes are represented by the following abbreviations: H (humped), P (positive), Ne (negative), U (U-shaped), and No (unrelated). (B) Sampling results of the shapes of SRPR based on the coefficient B representing the effect of tree diversity on forest productivity. Left: B values ranging from 0 to 1 correspond to positive and asymptotic shapes, while B ≤ 0 corresponds to level and negative shapes. Right: Dominance of different shapes based on the distribution of the sampling data. Tree diversity is represented by S , and productivity is represented by P . Adapted from Liang et al. (2016b) .

Another statistical dynamic model is the use of simple regression with empirical equations or direct regression analysis to demonstrate the different shapes of PRR based on field sampling results ( Axmanová et al., 2012 ; Steudel et al., 2012 ; Huang et al., 2018 ). In such models, the coefficient of species richness (independent variable) is utilized to determine the shapes of SRPR corresponding to the sampling results ( Figure 4B ). For instance, an empirical dynamical model P=α·f(X)·S B (P, productivity; X, environmental factors such as soil and climate; S, species richness; α, coefficient; B, the effects of species richness on productivity) was employed to quantify the dependence of productivity on species richness and measure the marginal productivity, which represents the change in productivity resulting from a one-unit decline in species richness, while accounting for climatic, soil, and plot-specific covariates ( Liang et al., 2016b ). When B > 1, the shape of SRPR is concave-down; when B = 1, the shape is positive; when 1 > B > 0, the shape is asymptotic; when B = 0, the shape is parallel (no effect); when B < 0, the shape is negative. Direct sampling data from various sources indicated that the average θ was 0.26, suggesting a predominantly positively asymptotic shape. Other forms occupied only a small percentage. A sampling study across the Amazon Basin, involving 90 one-hectare plots, also demonstrated the dominant positively asymptotic effect of taxonomic and evolutionary diversity on productivity, which was separated from environmental factors using generalized least-squares modeling ( De Souza et al., 2019 ). These field sampling results were consistent with meta-analyses of other ecologists’ studies, although meta-analysis represents a secondary form of sampling ( Hooper et al., 2005 ; Grace et al., 2007 ; Forrester & Bauhus, 2016 ; Duffy et al., 2017 ).

The statistical dynamical models based on field sampling are effective and straightforward approaches for identifying the shapes of PRR. Additionally, by utilizing a coefficient known as marginal productivity—the change in productivity resulting from a one-unit decline in species richness—the relationship between different shapes of PRR can be defined in a simple manner. However, these models have limited flexibility in considering variables other than productivity and species richness (represented by variable X). This limitation hinders the ability to reveal the interactions among these processes since X is often quantified using linear methods rather than non-linear ones ( Liang et al., 2016b ). In reality, the non-linear interactions of other processes significantly impact PRR, as demonstrated by earlier studies examining interactions among disturbance, competition, stress, resource availability, and more ( Grime, 1974 ; Huston, 1979 ; Hastings, 1980 ; Tilman, 1982 ). Unfortunately, the statistical dynamical models fail to adequately quantify these non-linear interactions of other processes, leading to increased errors in explaining the shapes of PRR.

Differential dynamical model

Some ecologists argue that PRR is governed by diverse and complex processes, and to clarify the shapes of PRR, it is necessary to assess the different effects of these processes on plant richness and productivity and simulate their interactions ( Willig, 2011 ; Grace et al., 2014 ; Wang, 2017 ). In line with this perspective, a set of differential equations, known as the PSRR model, was established based on the positive and/or negative effects of 21 widely accepted processes on plant productivity and species richness, as identified in the relevant literature ( Wang et al., 2019 ). These equations integrate the effects of these processes into a comprehensive measure of plant productivity, allowing for the derivation of the shapes of PSRR. Each process is assigned a different parameter value to represent its strength, and these parameter values can be adjusted to regulate the strengths of the processes. Plant richness is explicitly defined as a dependent variable, while plant productivity serves as an independent variable in the equations, quantifying the effects of plant productivity on species richness. Subsequently, the PSRR model is transformed into the SRPR model, which represents the feedback relationships to PSRR. In the SRPR model, plant productivity is determined as a dependent variable, and species richness as an independent variable. Using the PSRR model, the five typical shapes of PSRR, the dynamics of IICE ( Box 1 ), and the effects of the species pool on these shapes with increasing productivity were derived and verified using field data ( Wang et al., 2019 ; Figure 5 ). It was observed that the shapes of PSRR can change from one shape to another by altering the parameter values representing the strengths of the processes. Since the same set of parameters is used in the SRPR model, the diverse shapes of SRPR can also be derived. These derivations indicate that different strengths of processes acting on species richness and productivity give rise to different shapes of PSRR and SRPR. Specifically, when the integrated processes show a dominant positive effect, the shape of PSRR or SRPR is linear or asymptotic; when the integrated processes show a dominant negative effect, the shape of PSRR or SRPR is negative; and when the integrated processes successively show a dominant positive and negative effect, the shape of PSRR or SRPR is humped. These integrative methods can explain the documented PSRR and SRPR patterns observed in empirical studies conducted over several decades on various terrestrial, freshwater, and marine taxa from different regions of the world ( Mittelbach et al., 2003 ; Gillman & Wright, 2006 ; Whittaker, 2010 ; Grace et al., 2014 ; Liang et al., 2016b ; Fichtner et al., 2017 ). Furthermore, these results reveal the connections between the different shapes of PSRR and SRPR and the underlying processes ( Wang, 2017 ; Wang et al., 2019 ).

Figure 5 Typical Shapes of PSRR. (A1–E1) These curves represent the humped, asymptotic, positive, negative, and irregular shapes, respectively, derived by the PSRR model, which incorporates almost all processes affecting species richness. Adapted from Wang et al. (2019) . (A2–E2) These curves illustrate the dynamics of intra- and inter-specific competition effects (b) and the potential species-pool effect (Sp), which directly influence the shapes of PSRR. (A3–E3) These curves depict the observed species richness along a productivity gradient at a local plot across Germany, Czech Republic, Russia, USA, and Australia, respectively. The regression curves represent the results fitted based on these observed species richness and productivity. The fitted curves correspond to the outcomes obtained by fitting the observed data with the PSRR model. Notably, there was no significant difference between the fitted and observed species richness.

While the differential dynamical model offers a flexible solution for revealing the dynamical interactions of different processes affecting PRR and can elucidate the mechanisms underlying PRR, it is challenging to determine the coefficients of the numerous variables in the model. Moreover, the shapes of PRR derived or modeled using this non-linear differential model are generally diverse and require validation using field sampling data. Therefore, the structural equation model and statistical dynamical model can complement the limitations of the differential dynamical model within an integrative framework.

The recent integrative studies using statistical and differential dynamic models ( Cardinale et al., 2007 ; Liang et al., 2016a , b ; Wang et al., 2019 ) have improved the limited universality of results obtained by earlier studies that primarily integrated only a few processes to explain the accepted dominant shapes of PRR. The differential dynamical model provides insights into why and how the diverse PRR patterns discovered by statistical dynamical models based on meta-analysis and field sampling occur in the real world. Based on the differential dynamic model, it has been found that: (i) ecological processes that have a positive or negative effect on plant richness and productivity in PSRR and SRPR can vary temporally or spatially; (ii) processes that have a strongly positive effect at one productivity or richness level may have a weakly positive or negative effect at another level; and (iii) the integration of all positive and/or negative effects of processes, species richness, and plant productivity into a total effect (which continually changes but may be positive or negative) fundamentally determines the shapes of PSRR and SRPR ( Wang et al., 2019 ; Leclère et al., 2020 ). However, these integrative methods still require further improvement. Theoretically, integrative methods are based on the analysis of processes affecting plant richness and productivity to establish dynamical models of PRR ( Tilman et al., 1997 ; Loreau, 1998 ; Wang et al., 2019 ). The parameter values representing the effects of processes on PRR in dynamical models are often assumed and subjectively determined, although many derived PRR shapes have been validated by field data. Such an approach can influence the reliability of the derived PRR shapes. Therefore, within the framework of explaining PRR, we propose that the parameter values representing the effects of processes on PRR in the PRR dynamical models should be determined by quantifying the roles of different processes in the regulation of PPR in the field using a structural equation model ( Figure 1 ).

Conclusions

PRR has been a subject of extensive debate and research in ecology. Over time, research on PRR has progressed through distinct stages, including the identification of different PRR shapes, investigations of influencing processes, and integrative studies involving vegetation analysis, manipulation experiments, and theoretical analysis. The central focus of the debate has been on determining the dominant shapes of PRR and understanding the underlying mechanisms.

Recent integrative research, which involves analyzing and integrating the effects of respective processes influencing PRR, has revealed that the humped, asymptotic, positive, negative, and irregular shapes of PRR are interconnected. These shapes are not fixed, and one shape of PRR can transition into another. The balance between the positive and negative effects of different processes plays a crucial role in determining the various shapes of PRR. Furthermore, this balance leads to plant diversity having a globally positive effect on plant productivity and other ecosystem functions.

Respective and integrative research represent two types of methods employed to study the ecological processes influencing PRR. Respective research focuses on testing the effects of individual processes on PRR and uncovering the underlying mechanisms. Integrative research, on the other hand, examines the relative roles and interactions of processes in regulating PRR in real-world settings, as well as the relationships between different PRR shapes. PRR is considered a fundamental ecological issue that spans populations, communities, ecosystems, and landscapes. Ecologists have long been interested in PRR and the ecological processes that affect it, which has led to the development of various ecological theories.

Future studies on PRR should emphasize the relationships between metabolic rates related to resource availability and productivity, gene mutation rates, and increasing plant diversity, as these factors are evolutionarily significant. It is essential to identify the relative importance of each process and understand their interactions for the advancement of integrative studies. While significant progress has been made in understanding PRR, it is crucial for ecologists to carefully differentiate between the two types of PRR influenced by respective and integrative processes. Confusion between these types of PRR and different research methods can contribute to additional debates and challenges in the field.

Author contributions

ZW: Conceptualization, Funding acquisition, Methodology, Project administration, Software, Supervision, Validation, Writing – original draft, Writing – review & editing. JA: Software, Validation, Writing – review & editing. TY: Data curation, Methodology, Software, Writing – review & editing. CZ: Data curation, Formal Analysis, Writing – original draft. AC: Conceptualization, Supervision, Validation, Writing – review & editing.

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The work was supported by the Fundamental Research Funds for the central Universities (No.300111230018; No. 300102292902).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords: plant diversity, productivity, dynamical models, structural equation model, ecological processes, ecosystem functions, integrative research

Citation: Wang Z, Arratia J, Yan T, Zhang C and Chiarucci A (2024) Integrative framework of multiple processes to explain plant productivity–richness relationships. Front. Ecol. Evol. 12:1332985. doi: 10.3389/fevo.2024.1332985

Received: 04 November 2023; Accepted: 15 March 2024; Published: 04 April 2024.

Reviewed by:

Copyright © 2024 Wang, Arratia, Yan, Zhang and Chiarucci. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Zhenhong Wang, [email protected]

This article is part of the Research Topic

Insect Conservation Behavior

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How to Cite a Website | MLA, APA & Chicago Examples

Published on March 5, 2021 by Jack Caulfield . Revised on January 17, 2024.

To cite a page from a website, you need a short in-text citation and a corresponding reference stating the author’s name, the date of publication, the title of the page, the website name, and the URL.

This information is presented differently in different citation styles. APA , MLA , and Chicago are the most commonly used styles.

Use the interactive example generator below to explore APA and MLA website citations.

Note that the format is slightly different for citing YouTube and other online video platforms, or for citing an image .

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Table of contents

Citing a website in mla style, citing a website in apa style, citing a website in chicago style, frequently asked questions about citations.

An MLA Works Cited entry for a webpage lists the author’s name , the title of the page (in quotation marks), the name of the site (in italics), the date of publication, and the URL.

The in-text citation usually just lists the author’s name. For a long page, you may specify a (shortened) section heading to locate the specific passage. Don’t use paragraph numbers unless they’re specifically numbered on the page.

The same format is used for blog posts and online articles from newspapers and magazines.

You can also use our free MLA Citation Generator to generate your website citations.

Generate accurate MLA citations with Scribbr

Citing a whole website.

When you cite an entire website rather than a specific page, include the author if one can be identified for the whole site (e.g. for a single-authored blog). Otherwise, just start with the site name.

List the copyright date displayed on the site; if there isn’t one, provide an access date after the URL.

Webpages with no author or date

When no author is listed, cite the organization as author only if it differs from the website name.

If the organization name is also the website name, start the Works Cited entry with the title instead, and use a shortened version of the title in the in-text citation.

When no publication date is listed, leave it out and include an access date at the end instead.

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An APA reference for a webpage lists the author’s last name and initials, the full date of publication, the title of the page (in italics), the website name (in plain text), and the URL.

The in-text citation lists the author’s last name and the year. If it’s a long page, you may include a locator to identify the quote or paraphrase (e.g. a paragraph number and/or section title).

Note that a general reference to an entire website doesn’t require a citation in APA Style; just include the URL in parentheses after you mention the site.

You can also use our free APA Citation Generator to create your webpage citations. Search for a URL to retrieve the details.

Generate accurate APA citations with Scribbr

Blog posts and online articles.

Blog posts follow a slightly different format: the title of the post is not italicized, and the name of the blog is.

The same format is used for online newspaper and magazine articles—but not for articles from news sites like Reuters and BBC News (see the previous example).

When a page has no author specified, list the name of the organization that created it instead (and omit it later if it’s the same as the website name).

When it doesn’t list a date of publication, use “n.d.” in place of the date. You can also include an access date if the page seems likely to change over time.

In Chicago notes and bibliography style, footnotes are used to cite sources. They refer to a bibliography at the end that lists all your sources in full.

A Chicago bibliography entry for a website lists the author’s name, the page title (in quotation marks), the website name, the publication date, and the URL.

Chicago also has an alternative author-date citation style . Examples of website citations in this style can be found here .

For blog posts and online articles from newspapers, the name of the publication is italicized. For a blog post, you should also add the word “blog” in parentheses, unless it’s already part of the blog’s name.

When a web source doesn’t list an author , you can usually begin your bibliography entry and short note with the name of the organization responsible. Don’t repeat it later if it’s also the name of the website. A full note should begin with the title instead.

When no publication or revision date is shown, include an access date instead in your bibliography entry.

The main elements included in website citations across APA , MLA , and Chicago style are the author, the date of publication, the page title, the website name, and the URL. The information is presented differently in each style.

In APA , MLA , and Chicago style citations for sources that don’t list a specific author (e.g. many websites ), you can usually list the organization responsible for the source as the author.

If the organization is the same as the website or publisher, you shouldn’t repeat it twice in your reference:

• In APA and Chicago, omit the website or publisher name later in the reference.
• In MLA, omit the author element at the start of the reference, and cite the source title instead.

If there’s no appropriate organization to list as author, you will usually have to begin the citation and reference entry with the title of the source instead.

When you want to cite a specific passage in a source without page numbers (e.g. an e-book or website ), all the main citation styles recommend using an alternate locator in your in-text citation . You might use a heading or chapter number, e.g. (Smith, 2016, ch. 1)

In APA Style , you can count the paragraph numbers in a text to identify a location by paragraph number. MLA and Chicago recommend that you only use paragraph numbers if they’re explicitly marked in the text.

For audiovisual sources (e.g. videos ), all styles recommend using a timestamp to show a specific point in the video when relevant.

Check if your university or course guidelines specify which citation style to use. If the choice is left up to you, consider which style is most commonly used in your field.

• APA Style is the most popular citation style, widely used in the social and behavioral sciences.
• MLA style is the second most popular, used mainly in the humanities.
• Chicago notes and bibliography style is also popular in the humanities, especially history.
• Chicago author-date style tends to be used in the sciences.

Other more specialized styles exist for certain fields, such as Bluebook and OSCOLA for law.

The most important thing is to choose one style and use it consistently throughout your text.

Cite this Scribbr article

If you want to cite this source, you can copy and paste the citation or click the “Cite this Scribbr article” button to automatically add the citation to our free Citation Generator.

Caulfield, J. (2024, January 17). How to Cite a Website | MLA, APA & Chicago Examples. Scribbr. Retrieved April 2, 2024, from https://www.scribbr.com/citing-sources/cite-a-website/

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Daniel Kahneman, Nobel laureate who upended economics, dies at 90

He found that people rely on shortcuts that often lead them to make wrongheaded decisions that go against their own best interest.

Daniel Kahneman, an Israeli American psychologist and best-selling author whose Nobel Prize-winning research upended economics — as well as fields ranging from sports to public health — by demonstrating the extent to which people abandon logic and leap to conclusions, died March 27. He was 90.

His death was confirmed by his stepdaughter Deborah Treisman, fiction editor at the New Yorker. She did not say where or how he died.

Dr. Kahneman’s research was best known for debunking the notion of “homo economicus,” the “economic man” who since the epoch of Adam Smith was considered a rational being who acts out of self-interest. Instead, Dr. Kahneman found, people rely on intellectual shortcuts that often lead to wrongheaded decisions that go against their own best interest.

These misguided decisions occur because humans “are much too influenced by recent events,” Dr. Kahneman once said. “They are much too quick to jump to conclusions under some conditions and, under other conditions, they are much too slow to change.”

Dr. Kahneman was affiliated with Princeton University when he won the 2002 Nobel Memorial Prize in Economic Sciences “for having integrated insights from psychological research into economic science, especially concerning human judgment and decision-making under uncertainty.” He shared the award with Vernon L. Smith, then of George Mason University in Virginia, who pioneered the use of laboratory experiments in economics.

Dr. Kahneman took a dim view of people’s ability to think their way through a problem. “Many people are overconfident, prone to place too much faith in their intuitions,” he wrote in his popular 2011 book , “Thinking, Fast and Slow.” “They apparently find cognitive effort at least mildly unpleasant and avoid it as much as possible.”

Dr. Kahneman spent much of his career working alongside psychologist Amos Tversky, who he said deserved much of the credit for their prizewinning work. But Tversky died in 1996, and the Nobel is never awarded posthumously.

Both men were atheist grandsons of Lithuanian rabbis, and both had studied and lectured at the Hebrew University of Jerusalem. Their three-decade friendship and close collaboration, chronicled in Michael Lewis’s 2016 book, “The Undoing Project,” was a study in opposites.

According to Lewis, Tversky was the life of the party; Dr. Kahneman never even went. Tversky had a mechanical pencil on his desk and nothing else; Dr. Kahneman’s office was full of books and articles he never finished. Still, Dr. Kahneman said, at times it was as if “we were sharing a mind.” They worked so closely together that they tossed a coin to decide whose name would go first on an article or a book.

Their research helped establish the field of behavioral economics, which applies psychological insights to the study of economic decision-making, but also had a far-reaching effect outside the academy. It was credited with changing the way baseball scouts evaluate prospects, governments make public policy and doctors arrive at medical diagnoses.

Inspired in part by “Judgments Under Uncertainty,” an early paper by Dr. Kahneman and Tversky, economist Richard Thaler and legal scholar Cass Sunstein developed the concept of “libertarian paternalism.” Thaler and Sunstein’s 2008 book, “Nudge,” suggested ways that governments could encourage people to save for retirement, take care of their health and make other intelligent choices with minimal intrusion by authorities.

Dr. Kahneman presented his ideas to a general audience in “Thinking, Fast and Slow,” which distinguished between two modes of thought: System 1, in which the mind, acting quickly, relies on intuition, immediate impressions and emotional reactions; and System 2, in which the mind, slowing down, functions more rationally and analytically and is able to correct errors made by System 1.

Much of the time, Dr. Kahneman argued, the mind works in System 1 and draws conclusions using System 1’s toolbox: rules of thumb, cognitive biases and anything else that speeds up the judgment process.

Dr. Kahneman and Tversky did experiments that demonstrated various cognitive biases. They showed, for instance, that many more people were willing to make a 20-minute trip to save $5 on the price of a $15 calculator than to make the same trip to save the same amount of money, $5, on a $125 calculator — an example of what is known as the framing effect.

In another Kahneman-Tversky experiment, students were told about a fictitious Linda, 31, who was an activist in college and “was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.”

Then the students were asked which was more likely: that Linda is a bank teller or that Linda is a bank teller and is active in the feminist movement. The vast majority went with bank teller and active feminist, which has to be the less likely choice because the probability of two conditions will always be less than the probability of either one. This experiment demonstrated what is known as the conjunction fallacy, another way in which people sometimes fail to think logically.

One type of psychological distortion that occupied Dr. Kahneman in later years was the difference between “experienced” and “remembered” well-being and between experienced and remembered happiness or unhappiness. The remembered experience, he said, was largely determined by its most extreme moment, or peak, and by its end — hence the “peak-end rule.”

According to the rule, if we have a pleasurable experience at the end of a vacation, for instance, we tend to remember the entire holiday fondly. Similarly, if we feel less pain at the end of a medical procedure, we recall the entire experience as less painful. Sometimes, he found, the remembered experience is more important than the experience itself.

Daniel Kahneman was born in Tel Aviv on March 5, 1934, while his mother was visiting relatives in what was then the British mandate of Palestine. The Kahnemans made their home in France, and young Daniel was raised in Paris, where his mother was a homemaker and his father was the chief of research for a cosmetics firm.

During World War II, he was forced to wear a Star of David after Nazi German forces occupied the city in 1940. One night in 1941 or ’42, he later recalled, he stayed out past the German-imposed curfew for Jews while visiting a friend, and he turned his sweater inside out to hide the star while he walked a few blocks home. He then crossed paths with a soldier in the SS, who called him over, picked him up — and hugged him.

“I was terrified that he would notice the star inside my sweater,” Dr. Kahneman noted in a biographical essay for the Nobel Prize ceremonies. But the German pulled out his wallet, showed him a photo of a boy, gave him some money and sent him on his way. “I went home more certain than ever that my mother was right: people were endlessly complicated and interesting.”

As the Nazis stepped up the mass arrest of French Jews, Dr. Kahneman’s father narrowly escaped deportation to a death camp. The family fled to still-unoccupied Vichy France, where they eventually found refuge in a chicken coop in the seaside town of Cagnes-sur-Mer. In November 1942, the Germans took control of Vichy France.

As Lewis noted in his book, Dr. Kahneman had to hide in plain sight, attending school but avoiding social contact with teachers and classmates. While he found human personality intensely interesting, Lewis wrote, “his survival had depended on keeping himself apart.”

The Germans and their French collaborators stepped up the search for Jews in hiding. Dr. Kahneman’s father, a diabetic, found it increasingly difficult to secure medication and died of complications from the disease just six weeks before the Allied D-Day invasion. “I was really angry about his dying,” Dr. Kahneman told Lewis. “He had been good. But he had not been strong.”

After the war, Dr. Kahneman moved with his mother and sister to what soon became the state of Israel. At 15, he took a vocational test that said he had the makings of a psychologist. He graduated from Hebrew University in 1954 with a bachelor’s degree in psychology and mathematics. He fulfilled part of his military service requirement by devising character assessment tests for recruits.

In 1961, Dr. Kahneman received a doctorate in psychology from the University of California at Berkeley and returned to Hebrew University as a lecturer. There he met Tversky, who was gaining a reputation as one of the most brilliant psychologists of his generation.

Dr. Kahneman’s first marriage, to Irah Kahn, ended in divorce. In 1978, he wed Anne Treisman, a cognitive psychologist who studied mechanisms of perception and attention. They taught at the University of British Columbia and Berkeley before joining Princeton in 1993.

Meanwhile, Tversky took a position at Stanford University. The physical separation made cooperation with Dr. Kahneman difficult, if not impossible, and the friendship soured.

By the late 1980s, Dr. Kahneman had come to believe that Tversky did not sufficiently value his contributions to their work, and Tversky had his own complaints about Dr. Kahneman. “I sort of divorced him,” Dr. Kahneman later said . The two revived their friendship in the months before Tversky died of melanoma in 1996.

Treisman died in 2018 . Dr. Kahneman later lived with Barbara Tversky, the widow of his longtime collaborator.

In addition to Tversky, his partner of four years, survivors include two children from his first marriage, Michael Kahneman and Lenore Shoham; four stepchildren, Jessica, Daniel, Stephen and Deborah Treisman; and seven grandchildren.

Dr. Kahneman received the Presidential Medal of Freedom, the nation’s highest civilian honor, from President Barack Obama in 2013. An inveterate pessimist, he said he and his wife had not expected the Nobel, despite a raft of honors received over the years.

“We thought the probability was 0.2,” Treisman told the Philadelphia Inquirer after Dr. Kahneman’s award was announced. “We were quite interested to see who won.”