Twenty nine RCTs (n=2,052) were included in the review. Sample sizes ranged from 18 to 681 patients (most studies included fewer than 100 patients). The mean score for methodological rating was 19.6 (SD=4.9). Some studies did not include follow-up, while others ranged from two to 24 weeks follow-up.
The overall effect size for third wave studies was 0.56 (95% CI: 0.33, 0.79, p<0.0001), but there was evidence of significant heterogeneity (p<0.0001).
The mean overall effect size was moderate for ACT studies (13 RCTs) at 0.68 (95% CI: 0.42, 0.94, p<0.0001) and DBT studies (13 RCTs) at 0.58 (95% CI: 0.38, 0.77, p<0.0001), indicating greater treatment effects with interventions compared to controls. Effect sizes by comparison group were reported in the review. There was evidence of significant heterogeneity for ACT studies (p=0.006).
No studies on Functional Analytic Psychotherapy (FAP) were identified, and results for cognitive behavioural analysis system of psychotherapy (CBASP) (one RCT) and Integrative Behavioural Couple Therapy (IBCT) (two RCTs) were reported in the review. Fail-safe N using Orwin's test reported limited risk of publication bias for ACT and DBT studies.