How do I cite a series of booklets in APA Style?
If the factbooks were each written by different departments of the university and are treated as separate resources, you could use a multiple author citation to show that the information has been compiled from numerous sources. Please see "How do I format a multi-author in-text citation in APA Style?" for more information.
If the booklets are treated as separate resources, were all authored by the university, and were published in the same year, you'll need to distinguish between them in the in-text citations and cite each booklet separately in the references. Please see "How do I cite two or more resources by the same author that were published in the same year in APA style?".