A meta-analysis of nonrandomized effectiveness studies on outpatient cognitive behavioral therapy for adult anxiety disorders

The primary aim of this study was to assess the overall effectiveness of individual and group outpatient cognitive behavioral therapy (CBT) for adults with a primary anxiety disorder in routine clinical practice. We conducted a random effects meta-analysis of 71 nonrandomized effectiveness studies on outpatient individual and group CBT for adult anxiety disorders. Standardized mean gain effect sizes pre- to posttreatment, and posttreatment to follow-up are reported for disorder-specific symptoms, depression, and general anxiety. The mean dropout from CBT is reported. Outpatient CBT was effective in reducing disorder-specific symptoms in completer (d=0.90–1.91) and intention-to-treat samples (d=0.67–1.45). Moderate to large (d=0.54–1.09) and small to large effect sizes (d=0.42–0.97) were found for depressive and general anxiety symptoms posttreatment. Across all anxiety disorders, the weighted mean dropout rate was 15.06%. Posttreatment gains for disorder-specific anxiety were maintained 12months after completion of therapy. CBT for adult anxiety disorders is very effective and widely accepted in routine practice settings. However, the methodological and reporting quality of nonrandomized effectiveness studies must be improved. •Outpatient CBT is effective for adult anxiety disorders in clinical practice settings.•Posttreatment gains were maintained 3 and 12months after completion of therapy.•Dropout from treatment is moderate.•There is a need for high-quality effectiveness studies.