Answered By: Rachel Willard
Last Updated: May 02, 2017     Views: 2893

If you are citing two or more sources by the same author that were published in the same year, first alphabetize the sources by title, and then add the lowercase letters a, b, c, and so forth to the end of the publication years, starting with the first source. 

Reference Entries

Add the lowercase letter immediately after the publication year in reference entries. See the examples below for a list of reference entries that would need lowercase letters: 


  •    Centers for Disease Control and Prevention. (2011a). Birth defects. Retrieved from


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


  •    Centers for Disease Control and Prevention. (2011c). Prevent diabetes. Retrieved  from



*Be sure to insert a hanging indent for each reference entry. See the Academic Skills Center's Microsoft Word tutorials for APA formatting to learn how to create a hanging indent.


In-Text Citations

The lowercase letter is determined by the source's position in the reference list. Within in-text citations, use the author and year of publication, but keep the appropriate lowercase letter with the publication year.

  • Parenthetical:
    • Although not entirely preventable, mothers can try to avoid birth defects by taking folic acid, avoiding smoking, and not drinking alcohol (Center for Disease Control and Prevention, 2011a).
  • Within the Sentence:
    • According to the Center for Disease Control and Prevention (2011b), mothers can try to avoid birth defects by taking folic acid, avoiding smoking, and not drinking alcohol.


Additional Resources:

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Looking for more information? Learn more about reference list formatting or view tips on creating and using in-text citations.


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