What is the evidence for the efficacy of self-help Acceptance and Commitment Therapy? A systematic review and meta-analysis.

Acceptance and Commitment Therapy (ACT) is a form of psychotherapy with growing evidence for its transdiagnostic effects. Traditionally face-to-face, ACT is also delivered in self-help formats. As self-help is becoming more prevalent, the demand for empirical evidence of the efficacy of ACT self-help is increasing, and there are concerns that intervention outcomes are being 'over-sold'. A systematic search of the literature was conducted to find all peer-reviewed randomized controlled trials investigating the efficacy of ACT self-help on depression, anxiety, and/or psychological flexibility (PF). Thirteen studies were identified and reviewed, totaling 2580 participants. A quality appraisal of the papers under review indicated bias in methodology and reporting that may be limit the interpretability of existing evidence. Meta-analysis showed significant small effect sizes favoring intervention for depression (g=0.34; 95% CIs [0.07, 0.61]; Z=2.49, p=.01), anxiety (g=0.35; 95% CIs [0.09, 0.60]; Z=2.66, p=.008), and PF (g=0.42; 95% CIs [0.14, 0.70]; Z=2.93, p=.003) outcomes. Results indicate that higher levels of clinician guidance improves outcomes but that intervention format (e.g. book/computer) is unlikely to moderate results. Analysis also showed that increases in PF were associated with reductions in depression (rho=-.70, p=.25, n=10) and anxiety (rho=-.90, p<.001, n=10), giving initial support for the theory that changes in PF mediate distress outcomes. Therefore, ACT self-help may be a suitable intervention, particularly when clinician guidance is given. However, due to the small effect sizes, limited number of studies, and considerable heterogeneity of results, any conclusions made are tentative