The second problem we aimed to examine was the quality of trials. We found that the methodological quality in most studies was low or unknown. We evaluated the quality by the Cochrane “risk of bias” assessment tool, and found that across all disorders only 25 trials (17.4%) were rated as high-quality. The effect size was lower in high-quality studies for PAD (g50.61 compared to g50.81 in all studies) and SAD (g50.76 compared to g50.88 in all studies). We did not find strong indi- cations that the quality of trials was associated with the effect size in MDD and GAD. Although we did not find a strong asso- ciation between effect size and quality of trials for all disorders, the small number of high-quality studies still means that the overall effect sizes we found for all four disorders are uncertain.