Another limitation was the fact that it was possible to calculate a controlled effect size for only 16 of the 39 trials, and except for measures of anxiety symptom severity in active treatment controlled studies, the effect size estimates were not reliable due to a considerable publication bias. However, the pre-post treatment effects were robust and unlikely to be the result of a psychological placebo because the observed effect size is greater than what would be expected from a psychological placebo (Smits & Hofmann, 2009). Nevertheless, future studies are needed to clearly establish the efficacy of MBT in randomized controlled trials.
