The APA style manual does not have an example of how to cite dissertations in the ProQuest Dissertations and Theses database. A representative from APA recently posted the following to an inquiry on the EBSS (Educational, Behavioral & Social Sciences Librarians) listserv.
"The ProQuest Dissertations and Theses database appears to include dissertations abstracted in Dissertation Abstracts International. If the reference you are citing was abstracted in DAI but obtained from ProQuest (similar to Examples 54 and 55 in the Publication Manual), I would probably add that information to the reference entry as well:
Gibson, G. (2006). Between voice and silence: Identity development in Black adolescent females (Doctoral dissertation, State University of New York at Buffalo). Dissertation Abstracts International, 54, 100. Retrieved August 15, 2006, from ProQuest Dissertations and Theses database.
If there is no DAI information available, then you could simply skip right to the retrieval information."
