Citing Multiple Sources from an Author with the Same Year

You will need to differentiate between sources with the same author and publication date by adding a lower-case letter to the publication year. Including this lower-case letter ensures that the reader knows which source you are citing in-text and can find that source in your reference list.

Reference Entries

Add the lowercase letter immediately after the publication year in reference entries:

Centers for Disease Control and Prevention. (2011a). Birth defects. Retrieved April 26, 2011, from

Centers for Disease Control and Prevention. (2011b). Calcium and bone health. Retrieved April 26, 2011, from

Centers for Disease Control and Prevention. (2011c). Prevent diabetes. Retrieved April 26, 2011, from

*Note that we have listed these entries alphabetically by title, with the lower-case letters assigned based on this order.

In-Text Citations

Within in-text citations, you will keep the lowercase letter with the publication year:

(Center for Disease Control, 2011a) or According to the Center for Disease Control (2011b)



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In addition to the information provided here, refer to page 186 in the APA Manual (Sixth Edition) for how to cite and reference nonroutine information and titles. 

CDC website

Citing Yourself

Course Materials

Discussion Post

Dissertation or Thesis

DVD/Online Video

ERIC Document

eReader (Kindle, Nook, etc.)

Legal Material


Parts of a Book

Personal Communication

PowerPoint Presentation

Secondary Source

Sources with the Same Author and Same Year

Walden Course Catalog

You may also find our table on citation variations useful to download and print!