title: A meta-analysis of the efficacy of acceptance and commitment therapy for clinically relevant mental and physical health problems.
abstract: BACKGROUND
  The current study presents the results of a meta-analysis of 39 randomized controlled trials on the efficacy of acceptance and commitment therapy (ACT), including 1,821 patients with mental disorders or somatic health problems.
  
  
  METHODS
  We searched PsycINFO, MEDLINE and the Cochrane Central Register of Controlled Trials. Information provided by the ACBS (Association of Contextual Behavioral Science) community was also included. Statistical calculations were conducted using Comprehensive Meta-Analysis software. Study quality was rated using a methodology rating form.
  
  
  RESULTS
  ACT outperformed control conditions (Hedges' g = 0.57) at posttreatment and follow-up assessments in completer and intent-to-treat analyses for primary outcomes. ACT was superior to waitlist (Hedges' g = 0.82), to psychological placebo (Hedges' g = 0.51) and to treatment as usual (TAU) (we defined TAU as the standard treatment as usual; Hedges' g = 0.64). ACT was also superior on secondary outcomes (Hedges' g = 0.30), life satisfaction/quality measures (Hedges' g = 0.37) and process measures (Hedges' g = 0. 56) compared to control conditions. The comparison between ACT and established treatments (cognitive behavioral therapy) did not reveal any significant differences between these treatments (p = 0.140).
  
  
  CONCLUSIONS
  Our findings indicate that ACT is more effective than treatment as usual or placebo and that ACT may be as effective in treating anxiety disorders, depression, addiction, and somatic health problems as established psychological interventions. More research that focuses on quality of life and processes of change is needed to understand the added value of ACT and its transdiagnostic nature.
authors.affiliation: PsyQ, Zaandam, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Jacqueline G L
authors.initials: JG
authors.lastname: A-Tjak
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Davis
authors.forename: Nexhmedin
authors.initials: N
authors.lastname: Morina
authors.forename: Mark B
authors.initials: MB
authors.lastname: Powers
authors.forename: Jasper A J
authors.initials: JA
authors.lastname: Smits
authors.forename: Paul M G
authors.initials: PM
authors.lastname: Emmelkamp
mesh_terms: D064869:Acceptance and Commitment Therapy / Q000706:statistics & numerical data*; D001008:Anxiety Disorders / Q000628:therapy; D015928:Cognitive Behavioral Therapy / Q000379:methods*; D003863:Depression / Q000628:therapy; D006801:Humans; D011613:Psychotherapy / Q000379:methods*; D011788:Quality of Life; D016032:Randomized Controlled Trials as Topic