Psychological Medicine

Original Articles

A meta-analytic review of the effects of psychotherapy control conditions for anxiety disorders

J. A. J. Smitsa1 c1 and S. G. Hofmanna2

a1 Department of Psychology, Southern Methodist University, Dallas, TX, USA

a2 Department of Psychology, Boston University, Boston, MA, USA


Background Little is known about the magnitude of improvement associated with psychotherapy control conditions for adult anxiety disorders. This information is important for the design of psychosocial treatment efficacy studies.

Method We performed a computerized search of treatment outcome studies of anxiety disorders conducted between the first available year and 1 March 2007. In addition, we examined the reference lists from identified articles and asked international experts to identify eligible studies. We included studies that randomly assigned adult patients suffering from anxiety disorders to either cognitive–behavioral treatment or psychotherapy control condition. For each study, the two authors independently selected psychometrically sound measures of anxiety disorder severity. In addition, we collected data on attrition and treatment response.

Results Of the 1165 studies that were initially identified, 19 studies (454 patients) met inclusion criteria and were included in the analyses. The random effects analysis yielded a pre- to post-treatment Hedges' g effect size of 0.45 (95% confidence interval 0.35–0.46, z=8.50, p<0.001). The mean weighted response and attrition rates were 25.0% and 14.2%, respectively. There was no evidence for publication bias, nor was there a significant relationship between the effect size and diagnostic group, study year or number of treatment sessions.

Conclusions Psychotherapy control conditions are associated with significant improvements when administered to adults suffering from anxiety disorders. In addition, they are associated with a relatively low attrition rate. These findings can inform the design of future psychotherapy outcome studies.

(Received December 10 2007)

(Revised March 13 2008)

(Accepted March 15 2008)

(Online publication May 09 2008)


c1 Address for correspondence: J. A. J. Smits, Ph.D., Department of Psychology, Southern Methodist University, Dedman College, PO Box 750442, Dallas, TX 75275, USA. (Email: