title: A meta-analytic review of the effects of psychotherapy control conditions for anxiety disorders.
abstract: 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.
  
  
  METHODS
  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.
authors.affiliation: Department of Psychology, Southern Methodist University, Dallas, TX 75275, USA. jsmits@smu.edu
authors.forename: J A J
authors.initials: JA
authors.lastname: Smits
authors.forename: S G
authors.initials: SG
authors.lastname: Hofmann
mesh_terms: D001008:Anxiety Disorders / Q000628:therapy*; D006801:Humans; D011613:Psychotherapy / Q000379:methods*