If an author has multiple publications you need to cite, use a comma to separate the years of publication in chronological order (oldest to most recent). If the publications occur in the same year, the American Psychological Association Publication Manual recommends using suffixes a, b, c, etc.
NOTE: The corresponding letters should be used in the reference list, and these references should be ordered alphabetically by title.
Examples:
A recent study argued for the abolition of social class (Calvert, 2004, 2005a, 2005b).
Calvert (2004, 2005a, 2005b) argued for the abolition of social class.
