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Published on: September 12, 2014
Effect sizes of randomized-controlled studies of cognitive behavioral therapy for anxiety disorders over the past 30
Stefan G Hofmann1, Chantal Kasch1, Andreas Reis1
1Philipps-Universität Marburg, Germany.
Background:
Cognitive-behavioral therapy (CBT) is an effective treatment for the range of anxiety disorders as demonstrated in many randomized controlled trials (RCTs) conducted over the past 30 years.
Objective:
To examine the change of CBT effect sizes over time, we tested whether publication year was a significant moderator.
Data Sources:
We pooled studies from three previously published meta-analyses and searched three electronic databases (PubMed, PsychINFO, Web of Science) to identify any additional studies published from February 1, 2022 to January 24, 2025. The final analysis included 49 studies comprising a total of 3645 participants.
Study Selection:
We selected RCTs comparing CBT for anxiety disorders with psychological or pill control conditions.
Data Extraction:
Two independent raters used predefined data fields, including study quality indicators.
Data Synthesis:
The mean effect size of all RCTs comparing CBT vs. controls revealed a Hedges' g of 0.51, 95 % CI [0.40, 0.62], with significant differences in effect sizes between the diagnostic groups. Uncontrolled pre-post effect size calculations revealed a large effect for CBT, Hedges' g = 1.18, 95 % CI [1.01, 1.34], and a medium effect for the control conditions, Hedges' g = 0.59, 95 % CI [0.47, 0.70]. A linear meta-regression of publication year on effect sizes (Hedges g) showed no significant change in effect sizes as compared to the control conditions over the span of the last 30 years (B = -0.008, SE = 0.006, t(47) = -1.18, p = 0.24).
Conclusion:
Although CBT is an effective treatment for anxiety disorders, the effect sizes did not increase over the last 3 decades. This calls for studies on the processes of treatment change to improve the efficacy of CBT.
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