Figure 10.1 | Psychotherapy Versus No Treatment | These two normal distributions summarize the data of a meta-analysis of 475 studies on the effectiveness of psychotherapy. They show that psychotherapy is effective—the average psychotherapy client was better off than 80% of the people not receiving therapy.

(Data from Smith, M. L., Glass, G. V., & Miller, T. I. (1980). The benefits of psychotherapy. Baltimore, MD: Johns Hopkins University Press.