A meta-analysis of estimated effect sizes for group versus individual control treatments.

A meta-analysis was conducted combining results from nine studies, using seventy-five outcome measures of 349 subjects. Only studies that contrasted group, individual, and control treatments with a pretest-posttest design were selected. Estimates of effect sizes were calculated for group, individual, and control treatments across all studies, according to treatment modality (psychotherapy, counseling, or psychoeducation), type of control (no treatment or some treatment), date of the study (1955-1969 or 1977-1982), and the subjects' age (adult, adolescent, or child). Results indicated that both group and individual treatments had a measurable effect that was consistently greater than that of controls. Further, (1) counseling produced much more of an effect than either therapy or psychoeducation; (2) the more recent treatments produced larger effects than the older studies; and (3) group treatments were more effective than individual methods in the treatment of adolescents, but were less effective in the treatment of children.