The effect size observed for measures of depressive symptom severity for uncontrolled trials and MBT of controlled trials corresponded to a z-value of 21.82, indicating that 4,302 studies with an effect size of zero would be necessary to nullify this result (i.e., for the combined 2-tailed p-value to exceed .05). The fail-safe N for measures of anxiety disorder severity was 4,150 (z-value = 21.74). We also constructed funnel plots, which are depicted in Figures 2 and 3. Using the Trim and Fill method, the number of missing studies that would need to fall to the left of the mean effect size in order to make the plot symmetric was n = 7 studies for the analysis of anxiety measures and n = 10 for the analysis of depression measures. Assuming a random-effects model, the new imputed mean effect size was Hedges’ g = 0.51 (95% CI: .39-.63) for anxiety and Hedges’ g = 0.50 (95% CI: 0.42-.58) for depression. In sum, these analyses suggest that the effect size estimates of the pre-post analyses are unbiased.
