How To Use Et Al In A Research Paper

When writing research papers, most researchers would have come across the term “et al.” This is the abbreviation for a Latin phrase—written variously as et alii (masculine), et aliae (feminine), and et alia (neuter)—which means “and others.” The term “et al.” is mainly used for in-text citations of research papers having multiple authors, although some style guidelines also advocate the use of “et al.” in the reference list.

Ethical publication emphasizes that authors should provide an inclusive list of their sources in their manuscripts. This is because citations give credibility to a research work and help avoid plagiarism by crediting the original research work on which the present work is based. However, different journals and organizations follow different reference citation styles, which make it difficult to generalize the use of “et al.” when citing references.


Given below are a few citation style guidelines that outline the use of “et al.”

American Psychological Association (APA) Style Guide (6th edition): For references having three to five authors, APA states that all the author surnames (last names) should be cited at the first instance, and citations thereafter should include the first author’s surname followed by “et al.” But for research papers with six or more authors, the surname of the first author is always cited followed by “et al.” Note that “et al.” should not be in italics, and “al” should be followed by a period.

Example: Three to five authors, (Kernis, Cornell, Sun, Berry, & Hallow, 1993) or Kernis, Cornell, Sun, Berry, & Hallow (1993) will be used as the first citation, and (Kernis et al., 1993) or Kernis et al., (1993) should be used in subsequent citations.

Six or more authors: (Harris et al., 2001) or Harris et al. (2001)

Modern Language Association (MLA) Style Manual: For research papers having three or more authors, MLA states that, for the reference list, the first author’s surname should be cited, followed by a comma, then the rest of the name, followed by “et al.” For in-text citations, the first author’s surname is followed by “et al.”

Example: Russell, Tony, et al. (2016) for reference list; Russell et al. (2016) for in-text citation.

Chicago Manual of Style (CMS): For four to ten authors, write out all names in the bibliography but only the first author’s name followed by “et al.” in in-text citations.For more than ten authors, only the first seven are listed in the bibliography, but the first author’s name followed by “et al.” is used in in-text citations. Note that “et al.” is not italicized.

Example: Acoose et al. (2008) or (Acoose et al., 2008) for in-text citation.

As previously mentioned, different style guidelines have adopted different rules for using “et al.” So, the best way to use “et al.” is to check the guidelines of your target journal or organization and follow the style accordingly.

Citation–Sequence and Citation–Name

The following examples illustrate the citation–sequence and citation–name systems. The two systems are identical except for the order of references. In both systems, numbers within the text refer to the end references.

In citation–sequence, the end references are listed in the sequence in which they first appear within the text. For example, if a reference by Smith is the first one mentioned in the text, then the complete reference to the Smith work will be number 1 in the end references. The same number is used for subsequent in-text references to the same document.

In citation–name, the end references are listed alphabetically by author. Multiple works by the same author are listed alphabetically by title. The references are numbered in that sequence, such that a work authored by Adam is number 1, Brown is number 2, and so on. Numbers assigned to the end references are used for the in-text references regardless of the sequence in which they appear in the text of the work. For example, if a work by Zielinski is number 56 in the reference list, each in-text reference to Zielinski will be number 56 also.

Journals

List authors in the order in which they appear in the original text, followed by a period. Periods also follow article and journal title and volume or issue information. Separate the date from volume and issue by a semicolon. The location (usually the page range for the article) is preceded by a colon.

Author(s). Article title. Journal title. Date;volume(issue):location.

Journal titles are generally abbreviated according to the List of Title Word Abbreviations maintained by the ISSN International Centre. See Appendix 29.1 in Scientific Style and Format for more information.

For articles with more than 1 author, names are separated by a comma.

Smart N, Fang ZY, Marwick TH. A practical guide to exercise training for heart failure patients. J Card Fail. 2003;9(1):49–58.

For articles with more than 10 authors, list the first 10 followed by “et al.”

Pizzi C, Caraglia M, Cianciulli M, Fabbrocini A, Libroia A, Matano E, Contegiacomo A, Del Prete S, Abbruzzese A, Martignetti A, et al. Low-dose recombinant IL-2 induces psychological changes: monitoring by Minnesota Multiphasic Personality Inventory (MMPI). Anticancer Res. 2002;22(2A):727–732.

Volume with no issue or other subdivision

Laskowski DA. Physical and chemical properties of pyrethroids. Rev Environ Contam Toxicol. 2002;174:49–170.

Volume with issue and supplement

Gardos G, Cole JO, Haskell D, Marby D, Paine SS, Moore P. The natural history of tardive dyskinesia. J Clin Pharmacol. 1988;8(4 Suppl):31S–37S

Volume with supplement but no issue

Heemskerk J, Tobin AJ, Ravina B. From chemical to drug: neurodegeneration drug screening and the ethics of clinical trials. Nat Neurosci. 2002;5 Suppl:1027–1029.

Multiple issue numbers

Ramstrom O, Bunyapaiboonsri T, Lohmann S, Lehn JM. Chemical biology of dynamic combinatorial libraries. Biochim Biophys Acta. 2002;1572(2–3):178–186.

Issue with no volume

Sabatier R. Reorienting health and social services. AIDS STD Health Promot Exch. 1995;(4):1–3.

Books

Separate information about author(s), title, edition, and publication by periods. The basic format is as follows:

Author(s). Title. Edition. Place of publication: publisher; date. Extent. Notes.

Extent can include information about pagination or number of volumes and is considered optional. Notes can include information of interest to the reader, such as language of publication other than English; such notes are optional.

Essential notes provide information about location, such as a URL for online works. See Chapter 29 for more information.

For books with more than 1 author, names are separated by a comma.

Ferrozzi F, Garlaschi G, Bova D. CT of metastases. New York (NY): Springer; 2000.

For books with more than 10 authors, list the first 10 followed by “et al.”

Wenger NK, Sivarajan Froelicher E, Smith LK, Ades PA, Berra K, Blumenthal JA, Certo CME, Dattilo AM, Davis D, DeBusk RF, et al. Cardiac rehabilitation. Rockville (MD): Agency for Health Care Policy and Research (US); 1995.

Organization as author

Advanced Life Support Group. Acute medical emergencies: the practical approach. London (England): BMJ Books; 2001.

Author(s) plus editor(s) or translator(s)

Klarsfeld A, Revah F. The biology of death: origins of mortality. Brady L, translator. Ithaca (NY): Cornell University Press; 2003.

Luzikov VN. Mitochondrial biogenesis and breakdown. Galkin AV, translator; Roodyn DB, editor. New York (NY): Consultants Bureau; 1985.

Chapter or other part of a book, same author(s)

Gawande A. The checklist manifesto: how to get things right. New York (NY): Metropolitan Books; 2010. Chapter 3, The end of the master builder; p. 48–71.

Chapter or other part of a book, different authors

Rapley R. Recombinant DNA and genetic analysis. In: Wilson K, Walker J, editors. Principles and techniques of biochemistry and molecular biology. 7th ed. New York (NY): Cambridge University Press; 2010. p. 195–262.

Multivolume work as a whole

Alkire LG, editor. Periodical title abbreviations. 16th ed. Detroit (MI): Thompson Gale; 2006. 2 vol. Vol. 1, By abbreviation; vol. 2, By title.

Dissertations and Theses

Lutz M. 1903: American nervousness and the economy of cultural change [dissertation]. [Stanford (CA)]: Stanford University; 1989.

Patents

Blanco EE, Meade JC, Richards WD, inventors; Ophthalmic Ventures, assignee. Surgical stapling system. United States patent US 4,969,591. 1990 Nov 13.

Newspapers

Weiss R. Study shows problems in cloning people: researchers find replicating primates will be harder than other mammals. Washington Post (Home Ed.). 2003 Apr 11;Sect. A:12 (col. 1).

DVDs

Indicate a copyright date with a lowercase “c”.

Johnson D, editor. Surgical techniques in orthopaedics: anterior cruciate ligament reconstruction [DVD]. Rosemont (IL): American Academy of Orthopaedic Surgeons; c2002. 1 DVD.

Websites and Other Online Formats

References to websites and other online formats follow the same general principles as for printed references, with the addition of a date of update/revision (if available) along with an access date and a URL.

Website

Format:

Title of Homepage. Edition. Place of publication: publisher; date of publication [date updated; date accessed]. Notes.

If no date of publication can be determined, use a copyright date (if available), preceded by “c”. Include the URL in the notes.

APSnet: plant pathology. St Paul (MN): American Phytopathological Association; c1994–2005 [accessed 2005 Jun 20]. http://www.apsnet.org/.

Online journal article

Format:

Author(s) of article. Title of article. Title of journal (edition). Date of publication [date updated; date accessed];volume(issue):location. Notes.

A DOI (Digital Object Identifier) may be included in the notes in addition to a URL, if available:

Savage E, Ramsay M, White J, Beard S, Lawson H, Hunjan R, Brown D. Mumps outbreaks across England and Wales in 2004: observational study. BMJ. 2005 [accessed 2005 May 31];330(7500):1119–1120. http://bmj.bmjjournals.com/cgi/reprint/330/7500/1119. doi:10.1136/bmj.330.7500.1119.

e-Book

Format:

Author(s). Title of book. Edition. Place of publication: publisher; date of publication [date updated; date accessed]. Notes.

Example:

Brogden KA, Guthmille JM, editors. Polymicrobial diseases. Washington (DC): ASM Press; 2002 [accessed February 28, 2014]. http://www.ncbi.nlm.nih.gov/books/NBK2475/.

Blog

Format:

Author’s name. Title of post [descriptive word]. Title of blog. Date of publication. [accessed date]. URL.

Example:

Fogarty M. Formatting titles on Twitter and Facebook [blog]. Grammar Girl: Quick and Dirty Tips for Better Writing. 2012 Aug 14. [accessed 2012 Oct 19]. http://grammar.quickanddirtytips.com/formatting-titles-on-twitter-and-facebook.aspx.

Forthcoming or Unpublished Material

Not all forthcoming or unpublished sources are suitable for inclusion in reference lists. Check with your publisher if in doubt.

Forthcoming journal article or book

Journal article:

Farley T, Galves A, Dickinson LM, Perez MJ. Stress, coping, and health: a comparison of Mexican immigrants, Mexican-Americans, and non-Hispanic whites. J Immigr Health. Forthcoming 2005 Jul.

Book:

Goldstein DS. Adrenaline and the inner world: an introduction to scientific integrative medicine. Baltimore (MD): Johns Hopkins University Press. Forthcoming 2006.

Paper or poster presented at meeting

Unpublished presentations are cited as follows:

Antani S, Long LR, Thoma GR, Lee DJ. Anatomical shape representation in spine x-ray images. Paper presented at: VIIP 2003. Proceedings of the 3rd IASTED International Conference on Visualization, Imaging and Image Processing; 2003 Sep 8–10; Benalmadena, Spain.

Charles L, Gordner R. Analysis of MedlinePlus en Español customer service requests. Poster session presented at: Futuro magnifico! Celebrating our diversity. MLA ’05: Medical Library Association Annual Meeting; 2005 May 14–19; San Antonio, TX.

References to published presentations are cited much like contributions to books, with the addition of information about the date and place of the conference. See Chapter 29 for more information.

Personal communication

References to personal communication are placed in running text rather than as formal end references.

Permission is usually required and should be acknowledged in an “Acknowledgment” or “Notes” section at the end of the document.

. . . and most of these meningiomas proved to be inoperable (2003 letter from RS Grant to me; unreferenced, see “Notes”) while a few were not.

Name–Year

The following examples illustrate the name–year system. In this system (sometimes called the Harvard system), in-text references consist of the surname of the author or authors and the year of publication of the document. End references are unnumbered and appear in alphabetical order by author and year of publication, with multiple works by the same author listed in chronological order.

Each example of an end reference is accompanied here by an example of a corresponding in-text reference. For more details and many more examples, see Chapter 29 of Scientific Style and Format.

Journals

For the end reference, list authors in the order in which they appear in the original text. The year of publication follows the author list. Use periods to separate each element, including author(s), date of publication, article and journal title, and volume or issue information. Location (usually the page range for the article) is preceded by a colon.

Author(s). Date. Article title. Journal title. Volume(issue):location.

Journal titles are generally abbreviated according to the List of Title Word Abbreviations maintained by the ISSN International Centre. See Appendix 29.1 in Scientific Style and Format for more information.

For the in-text reference, use parentheses and list author(s) by surname followed by year of publication.

(Author(s) Year)

For articles with 2 authors, names are separated by a comma in the end reference but by “and” in the in-text reference.

Mazan MR, Hoffman AM. 2001. Effects of aerosolized albuterol on physiologic responses to exercise in standardbreds. Am J Vet Res. 62(11):1812–1817.

(Mazan and Hoffman 2001)

For articles with 3 to 10 authors, list all authors in the end reference; in the in-text reference, list only the first, followed by “et al.”

Smart N, Fang ZY, Marwick TH. 2003. A practical guide to exercise training for heart failure patients. J Card Fail. 9(1):49–58.

(Smart et al. 2003)

For articles with more than 10 authors, list the first 10 in the end reference, followed by “et al.”

Pizzi C, Caraglia M, Cianciulli M, Fabbrocini A, Libroia A, Matano E, Contegiacomo A, Del Prete S, Abbruzzese A, Martignetti A, et al. 2002. Low-dose recombinant IL-2 induces psychological changes: monitoring by Minnesota Multiphasic Personality Inventory (MMPI). Anticancer Res. 22(2A):727–732.

(Pizzi et al. 2002)

Volume with no issue or other subdivision

Laskowski DA. 2002. Physical and chemical properties of pyrethroids. Rev Environ Contam Toxicol. 174:49–170.

(Laskowski 2002)

Volume with issue and supplement

Gardos G, Cole JO, Haskell D, Marby D, Paine SS, Moore P. 1988. The natural history of tardive dyskinesia. J Clin Pharmacol. 8(4 Suppl):31S–37S.

(Gardos et al. 1988)

Volume with supplement but no issue

Heemskerk J, Tobin AJ, Ravina B. 2002. From chemical to drug: neurodegeneration drug screening and the ethics of clinical trials. Nat Neurosci. 5 Suppl:1027–1029.

(Heemskerk et al. 2002)

Multiple issue numbers

Ramstrom O, Bunyapaiboonsri T, Lohmann S, Lehn JM. 2002. Chemical biology of dynamic combinatorial libraries. Biochim Biophys Acta. 1572(2–3):178–186.

(Ramstrom et al. 2002)

Issue with no volume

Sabatier R. 1995. Reorienting health and social services. AIDS STD Health Promot Exch. (4):1–3.

(Sabatier 1995)

Books

In the end reference, separate information about author(s), date, title, edition, and publication by periods. The basic format is as follows:

Author(s). Date. Title. Edition. Place of publication: publisher. Extent. Notes.

Extent can include information about pagination or number of volumes and is considered optional. Notes can include information of interest to the reader, such as language of publication other than English; such notes are optional. Essential notes provide information about location, such as a URL for online works. See Chapter 29 for more information.

For books with 2 authors, names are separated by a comma in the end reference but by “and” in the in-text reference.

Leboffe MJ, Pierce BE. 2010. Microbiology: laboratory theory and application. Englewood (CO): Morton Publishing Company.

(Leboffe and Pierce 2010)

For books with 3 to 10 authors, list all authors in the end reference; in the in-text reference, list only the first, followed by “et al.”

Ferrozzi F, Garlaschi G, Bova D. 2000. CT of metastases. New York (NY): Springer.

(Ferrozzi et al. 2000)

For books with more than 10 authors, list the first 10 in the end reference, followed by “et al.”

Wenger NK, Sivarajan Froelicher E, Smith LK, Ades PA, Berra K, Blumenthal JA, Certo CME, Dattilo AM, Davis D, DeBusk RF, et al. 1995. Cardiac rehabilitation. Rockville (MD): Agency for Health Care Policy and Research (US).

(Wenger et al. 1995)

Organization as author

[ALSG] Advanced Life Support Group. 2001. Acute medical emergencies: the practical approach. London (England): BMJ Books.

(ALSG 2001)

Author(s) plus editor(s) or translator(s)

Klarsfeld A, Revah F. 2003. The biology of death: origins of mortality. Brady L, translator. Ithaca (NY): Cornell University Press.

Luzikov VN. 1985. Mitochondrial biogenesis and breakdown. Galkin AV, translator; Roodyn DB, editor. New York (NY): Consultants Bureau.

(Klarsfeld and Revah 2003)

(Luzikov 1985)

Chapter or other part of a book, same author(s)

Gawande A. 2010. The checklist manifesto: how to get things right. New York (NY): Metropolitan Books. Chapter 3, The end of the master builder; p. 48–71.

(Gawande 2010)

Chapter or other part of a book, different authors

Rapley R. 2010. Recombinant DNA and genetic analysis. In: Wilson K, Walker J, editors. Principles and techniques of biochemistry and molecular biology. 7th ed. New York (NY): Cambridge University Press. p. 195–262.

(Rapley 2010)

Multivolume work as a whole

Alkire LG, editor. 2006. Periodical title abbreviations. 16th ed. Detroit (MI): Thompson Gale. 2 vol. Vol. 1, By abbreviation; vol. 2, By title.

(Alkire 2006)

Dissertations and Theses

Lutz M. 1989. 1903: American nervousness and the economy of cultural change [dissertation]. [Stanford (CA)]: Stanford University.

(Lutz 1989)

Patents

Blanco EE, Meade JC, Richards WD, inventors; Ophthalmic Ventures, assignee. 1990 Nov 13. Surgical stapling system. United States patent US 4,969,591.

(Blanco et al. 1990)

Newspapers

Weiss R. 2003 Apr 11. Study shows problems in cloning people: researchers find replicating primates will be harder than other mammals. Washington Post (Home Ed.). Sect. A:12 (col. 1).

(Weiss 2003)

DVDs

Indicate a copyright date with a lowercase “c”.

Johnson D, editor. c2002. Surgical techniques in orthopaedics: anterior cruciate ligament reconstruction [DVD]. Rosemont (IL): American Academy of Orthopaedic Surgeons. 1 DVD.

(Johnson c2002)

Websites and Other Online Formats

References to websites and other online formats follow the same general principles as for printed references, with the addition of a date of update/revision (if available) along with an access date and a URL.

Website

Format for end reference:

Title of Homepage. Date of publication. Edition. Place of publication: publisher; [date updated; date accessed]. Notes.

If no date of publication can be determined, use a copyright date (if available), preceded by “c”. Include the URL in the notes.

APSnet: plant pathology online. c1994–2005. St Paul (MN): American Phytopathological Association; [accessed 2005 Jun 20]. http://www.apsnet.org/.

For the in-text reference, include only the first word or two of the title (enough to distinguish it from other titles in the reference list), followed by an ellipsis.

(APSnet . . . c1994–2005)

Online journal article

Format for end reference:

Author(s) of article. Date of publication. Title of article. Title of journal (edition). [date updated; date accessed];Volume(issue):location. Notes.

A DOI (Digital Object Identifier) may be included in the notes in addition to a URL, if available:

Savage E, Ramsay M, White J, Beard S, Lawson H, Hunjan R, Brown D. 2005. Mumps outbreaks across England and Wales in 2004: observational study. BMJ. [accessed 2005 May 31];330(7500):1119–1120. http://bmj.bmjjournals.com/cgi/reprint/330/7500/1119. doi:10.1136/bmj.330.7500.1119.

(Savage et al. 2005)

e-Book

Format for end reference:

Author(s). Date of publication. Title of book. Edition. Place of publication: publisher; [date updated; date accessed]. Notes.

Example:

Brogden KA, Guthmille JM, editors. 2002. Polymicrobial diseases. Washington (DC): ASM Press; [accessed February 28, 2014]. http://www.ncbi.nlm.nih.gov/books/NBK2475/.

(Brogden and Guthmille 2002)

Blog

Format for end reference:

Author’s name. Date of publication. Title of post [descriptive word]. Title of blog. [accessed date]. URL.

Example:

Fogarty M. 2012 Aug 14. Formatting titles on Twitter and Facebook [blog]. Grammar Girl: Quick and Dirty Tips for Better Writing. [accessed 2012 Oct 19]. http://grammar.quickanddirtytips.com/formatting-titles-on-twitter-and-facebook.aspx.

(Fogarty 2012)

Forthcoming or Unpublished Material

Not all forthcoming or unpublished sources are suitable for inclusion in reference lists. Check with your publisher if in doubt.

Forthcoming journal article or book

Journal article:

Farley T, Galves A, Dickinson LM, Perez MJ. Forthcoming 2005 Jul. Stress, coping, and health: a comparison of Mexican immigrants, Mexican-Americans, and non-Hispanic whites. J Immigr Health.

(Farley et al. 2005)

Book:

Goldstein DS. Forthcoming 2006. Adrenaline and the inner world: an introduction to scientific integrative medicine. Baltimore (MD): Johns Hopkins University Press.

(Goldstein 2006)

Paper or poster presented at meeting

Unpublished presentations are cited as follows:

Antani S, Long LR, Thoma GR, Lee DJ. 2003. Anatomical shape representation in spine x-ray images. Paper presented at: VIIP 2003. Proceedings of the 3rd IASTED International Conference on Visualization, Imaging and Image Processing; Benalmadena, Spain.

Charles L, Gordner R. 2005. Analysis of MedlinePlus en Español customer service requests. Poster session presented at: Futuro magnifico! Celebrating our diversity. MLA ’05: Medical Library Association Annual Meeting; San Antonio, TX.

(Atani et al. 2003)

(Charles and Gordner 2005)

References to published presentations are cited much like contributions to books, with the addition of information about the date and place of the conference. See Chapter 29 for more information.

Personal communication

References to personal communication are placed in running text rather than as formal end references. Permission is usually required and should be acknowledged in an “Acknowledgment” or “Notes” section at the end of the document.

. . . and most of these meningiomas proved to be inoperable (2003 letter from RS Grant to me; unreferenced, see “Notes”) while a few were not.

One thought on “How To Use Et Al In A Research Paper

Leave a Reply

Your email address will not be published. Required fields are marked *