From the AJPA Citation Guide:
Literature cited. In the text, references to the literature should be cited by author's surname followed by year of publication. If there are multiple citations, present them alphabetically:
. . . analysis by Ward (2001) reveal . . .
. . . studies by Corner and Richtsmeier (2004) reveal . . .
. . . studies by Little et al. (1993) reveal . . .
. . . an earlier report (Hutchinson, 1999) . . .
. . . earlier reports (Arriaza et al., 2000; Paoli et al., 2002; Ross, 2003) . . .
Use of et al. is determined by the number of authors and whether it is the first time a reference has been cited in the paper. Specifically, articles with one or two authors include all names in every in-text citation; articles with three, four, or five authors include all names in the first in-text citation but are abbreviated to the first author name plus et al. upon subsequent citations; and articles with six or more authors are abbreviated to the first author name plus et al. for all in-text citations.
When references are made to more than one paper by the same author published in the same year, they should be designated in the text as (Benefit and McCrossin, 1993a,b) and in the Literature Cited as follows:
Benefit B.R., McCrossin M.L. (1993a). New Kenyapithecus postcrania and other primate fossils from Maboko Island, Kenya [abstract]. American Journal of Physical Anthropology Suppl,16,55–56.
Benefit B.R., McCrossin M.L. (1993b). On the lacrimal fossa of Cercopithecinae, with special reference to cladistic analysis of Old World monkey relationships. Folia Primatologica, 60, 133–145.
The literature list must follow APA style (refer to the APA Style Manual, 6th edition) and be arranged alphabetically, not chronologically, by author's or authors' surname(s) in the following style: Author's name (or names), year of publication, complete title, volume, and inclusive pages as follows:
Eck, J., & Spelman, W. (1987). Problem-solving: Problem-oriented policing in Newport News. Research in Brief. Cambridge, England: National Institute of Justice.
Goldstein, H. (1990). Problem-oriented policing. New York, NY: McGraw-Hill.
Gilbert, D. G., McClernon, J. F., Rabinovich, N. E., Sugai, C., Plath, L. C., Asgaard, G., ... Botros, N. (1983). Situational crime prevention: Its theoretical basis and practical scope. In M. Tonry & N. Morris (Eds.), Crime and justice: An annual review of research (Vol. 4, pp. 225–256). Chicago, IL: University of Chicago Press.
Goldstein, H. (1979, Winter). Improving police: A problem-oriented approach. Crime & Delinquency, 3, 236–258.
Weiss, A., & McGarrell, E. F. (1996, November). The impact of increased traffic enforcement on crime. Paper presented at the annual meeting of the American Society of Criminology, Chicago, IL.
Muellbauer, J. (2007, September). Housing, credit, and consumer expenditure. In S. C. Ludvigson (Chair), Housing and consumer behavior. Symposium conducted at the meeting of the Federal Reserve Bank of Kansas City, Jackson Hole, WY.
Conference paper abstract retrieved online:
Liu, S. (2005, May). Defending against business crises with the help of intelligent agent based early warning solutions. Paper presented at the Seventh International Conference on Enterprise Information Systems, Miami, FL. Abstract retrieved from http://www.iceis.org/iceis2005/abstracts_2005.htm
Proceedings published in book form:
Katz, I., Gabayan, K., & Aghajan, H. (2007). A multi-touch surface using multiple cameras. In J. Blanc-Talon, W. Philips, D. Popescu, & P. Scheunders (Eds.), Lecture Notes in Computer Science: Vol. 4678. Advanced Concepts for Intelligent Vision Systems (pp. 97–108). Berlin, Germany: Springer-Verlag. doi:10.1007/978-3-540-74607-2
Schnittker, J. (2004). Education and the changing shape of the income gradient in health(Unpublished doctoral dissertation or master’s thesis). Name of Institution, Location.
Muthen, L. K., & Muthen, B. O. (2004). Child care and child development (Report No. xxx). Los Angeles, CA: Publisher.
Smith I. M. (2011). U. S. Patent No. 235,445. Location: Publisher.
Abbreviations of journal titles should follow those used in Index Medicus, available via PubMed athttp://www.ncbi.nlm.nih.gov/journals.
Notes: Alphabetize by the author’s surname. • Alphabetize letter by letter. When alphabetizing surnames, remember that “nothing precedes something”: Brown, J. R., precedes Browning, A. R., even though i precedes j in the alphabet. • Up to seven authors in the list. If more than seven, list first six and then ellipses followed by last author.