Meta-analysis is a new statistical technique used to integrate the results of many separate studies of a topic. The author, along with two colleagues, applied meta-analysis to 475 studies of the effectiveness of psychotherapy and 112 studies of the comparative effects of psychotherapy and psychoactive drugs. The investigators examined the studies' effect sizes--the standard mean difference on the outcome variable between the treated group and the comparison group. Since many studies had more than one outcome variable, the 475 studies actually produced 1,766 effect sizes. Meta-analysis of these data shows that psychotherapy is effective in enhancing psychological well-being, however it is measured by researchers. The patient's age and diagnosis, the therapist's training and experience, and the duration and mode of therapy bear little relation to the psychotherapy's outcome. Behavioral therapies are somewhat more effective than verbal ones, and drug therapy, while combining well with psychotherapy, is not more effective than psychotherapy alone.