Chris would like to conduct a study on the effectiveness of a new substance-abuse treatment program.

Chris would like to conduct a study on the effectiveness of a new substance-abuse treatment program. He has a sample of participants go through the program and he uses as a comparison group people who did not volunteer for the program but were eligible. Chris has used a(n) _________ design for his study.

a.nonequivalent group

b.interrupted time-series

c.pretest-posttest control-group

d.Solomon four-group