Smith, M.L., & Glass, G.V. (1977). Meta-Analysis Of Psychotherapy Outcome Studies. American Psychologist, Vol 32(9). 752-760.
Results of 375 controlled evaluations of psychotherapy and counseling wee coded and integrated statistically. The findings provide convincing evidence of the efficacy of psychotherapy. On the average, the typical therapy client is better off than 75% of untreated individuals. Few important differences in effectiveness could be established among many quite different types of psychotherapy. More generally, virtually no difference in effectiveness was observed between the class of all behavioral therapies (e.g., systematic desensitization and behavior modification) and the non-behavioral therapies (e.g., Rogerian, psychodynamic, rational-emotive, and transactional analysis). (PsycINFO Database Record © 2016, APA, all rights reserved)