To examine long-term outcome, we further conducted an effect size analysis for MBT from pre-treatment to the last available follow-up point. A total of nineteen studies reported follow-up data for measures of anxiety or depression symptoms. The mean length of follow-up was 27 weeks (SD = 32), with a median of 12 weeks. Seventeen studies reported follow-up data for anxiety measures. The effect size for the pooled data was Hedges’ g = 0.60 (95% CI: 0.48-0.71, p < .001). Eighteen studies reported follow-up data for depression measures. The effect size for this pooled data was Hedges’ g = 0.60 (95% CI: 0.48-0.72, p < .001). The fail-safe N for measures of anxiety symptoms at follow-up was 806 (z-value = 13.63), and of depression symptoms at follow-up was 952 (z-value = 14.38), suggesting that both effect size estimates can be considered robust.
