A group that provides a basis for contrast with a treatment group (i.e., the group of people participating in the program, project, or other intervention being evaluated). The comparison group is not subjected to the intervention (independent variable) or is subjected to another type of treatment thus creating a means for comparison with the group that does receive the intervention of interest.
Yarbrough, D. B., Shulha, L. M., Hopson, R. K., and Caruthers, F. A. (2011). The program evaluation standards: A guide for evaluators and evaluation users (3rd ed.). Thousand Oaks, CA: Sage.