When citing multiple authors for the same information, use semicolons to separate the different citations. The authors should be cited in alphabetical order, and, if there is a need to cite more than one source by the same author within a citation for multiple publications, place the years of publication in chronological order (oldest to most recent).
Example:
A recent study argued for the abolition of social class (Calvert, 1987; Liu, 2004, 2005; Smith, 2003).