Sixteen of the identified studies included a control or comparison group. Eight of these studies compared a MBT to a waitlist control, 3 to treatment-as-usual (TAU), and 5 to an active treatment comparison. Because patients in the waitlist control conditions typically received treatment-as-usual, we pooled together studies employing a waitlist control condition with those employing a TAU control condition. The random-effects analysis of the controlled studies employing a waitlist or TAU comparison condition yielded a mean Hedges’ g effect size of 0.41 (95% CI: 0.23-0.59, z = 4.35, p < .01) for continuous measures of depressive symptom severity, and 0.33 (95% CI: 0.11-0.54, z = 2.97, p < .01) for anxiety symptom severity. The random-effects analysis of the controlled studies employing an active treatment comparison condition yielded a mean Hedges’ g effect size of 0.50 (95% CI: 0.26-0.74, z = 4.06, p < .01) for continuous measures of depressive symptom severity, and 0.81 (95% CI: 0.35-1.27, z = 3.47, p < .01) for anxiety symptom severity. However, the fail-safe Ns for controlled studies for measures of depression and anxiety disorder
