Bibliography Same Author Different Years

Order the citations of two or more works by different authors within the same parentheses alphabetically in the same order in which they appear in the reference list (including citations that would otherwise shorten to et al.). Separate the citations with semicolons.

Example:
Several studies (Miller, 1999; Shafranske & Mahoney, 1998)

Arrange two or more works by the same authors (in the same order) by year of publication. Place in-press citations last. Give the authors' surnames once; for each subsequent work, give only the date.

Example:
Past research (Gogel, 1990, 2006, in press)

Identify works by the same author (or by the same two or more authors in the same order) with the same publication date by the suffixes a, b, c, and so forth, after the year; repeat the year. The suffixes are assigned in the reference list, where these kinds of references are ordered alphabetically by title (of the article, chapter, or complete work).

Example:
Several studies (Derryberry & Reed, 2005a, 2005b, in press-a; Rothbart, 2003a, 2003b)

Exception: You may separate a major citation from other citations within parentheses by inserting a phrase such as see also, before the first of the remaining citations, which should be in alphabetical order.

Example:
(Minor, 2001; see also Adams, 1999; Storandt, 2007)

(adapted from the sixth edition of the APA Publication Manual, © 2010)


by Chelsea Lee

Have you ever been friends with a pair of identical twins? Twins who looked so alike that, at first, telling them apart all hinged on finding that distinguishing freckle, or hoping someone else would call them by their names so you could memorize what clothes each was wearing that day? In the social sciences, there is a longstanding tradition of twin research, but this post refers to twins of another kind: reference twins. Specifically, this post addresses how to cite multiple articles by the same authors that were published in the same year so that everyone can easily tell them apart.

A Solution for Identical Twins

In essence, the solution to the reference twin problem is not much different from how twins are told apart at birth: Just as twins are referred to as “Baby A” and “Baby B,” “twin references” are also given letters to tell them apart. Specifically, lowercase letters are added after the year (2011a, 2011b, etc.), and the references are alphabetized by title to determine which is “a” and which is “b.” Here is an example:

Koriat, A. (2008a). Easy comes, easy goes? The link between learning and remembering and its exploitation in metacognition. Memory & Cognition, 36, 416–428. doi:10.3758/MC.36.2.416
Koriat, A. (2008b). Subjective confidence in one’s answers: The consensuality principle. Journal of Experimental Psychology: Learning, Memory, and Cognition, 34, 945–959. doi:10.1037/0278-7393.34.4.945

In the text, citations would be styled as follows: (Koriat, 2008a) and (Koriat, 2008b).

For references that are in press or that have no date (signified by n.d., which stands for “no date”), use the following forms for the date: (in press-a), (in press-b), (n.d.-a), and (n.d.-b), and so forth.

A Solution for Not-Quite Twins

However, be careful that your references are true identical twins. That is, the method described above applies only when all author names are the same and appear in the same order. If any of the names or the order is different, then the references are distinguished in a different way: by spelling out as many author names as necessary to tell them apart.  Let’s use the following two references as an example:

Marewski, J. N., Gaissmaier, W., & Gigerenzer, G. (2010). Good judgments do not require complex cognition. Cognitive Processing, 11, 103–121. doi:10.1007/s10339-009-0337-0
Marewski, J. N., Gaissmaier, W., Schooler, L. J., Goldstein, D. G., & Gigerenzer, G. (2010). From recognition to decisions: Extending and testing recognition-based models for multi-alternative inference. Psychonomic Bulletin & Review, 17, 287–309. doi:10.3758/PBR.17.3.287

The first in-text citations to each of these articles would be as follows:

  • (Marewski, Gaissmaier, & Gigerenzer, 2010)
  • (Marewski, Gaissmaier, Schooler, Goldstein, & Gigerenzer, 2010)

Now, what about subsequent in-text citations? Usually we would abbreviate studies with three or more authors to the first author name plus et al. (Latin for “and others”); however, doing so here would produce two Marewski et al. (2010) citations, leaving the reader unable to tell which one you mean. The solution is to spell out as many names as necessary (here, to the third name) upon subsequent citations to tell the two apart: 

  • (Marewski, Gaissmaier, & Gigerenzer, 2010)
  • (Marewski, Gaissmaier, Schooler, et al., 2010)

Notice that for the first reference, this means that all citations to this source will include all three names. For the second reference, the two remaining names can be abbreviated to et al. (Note, however, that if only one name remains to distinguish the references, that name must be spelled out with all the rest because et al. is plural—it cannot stand for only one name. This topic will be elaborated upon in an upcoming post.)

For more information and examples of citing references in text, see Chapter 6 of our sixth edition Publication Manual (pp. 174–179). You may also be interested in our primer on how in-text citations work.

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