Waiting list may be a nocebo condition in psychotherapy trials: a contribution from network meta‐analysis

TLDR

Control conditions in psychotherapy trials are increasingly suspected of producing varying effect size estimates. The study investigates how waiting list, no treatment, and psychological placebo differ as control conditions. Researchers performed a comprehensive search of RCTs on CBT for acute depression and applied network meta‑analysis to integrate direct and indirect comparisons. The analysis of 49 trials (2730 participants) revealed that CBT’s effect size varied by control condition, with no‑treatment showing a 2.9‑fold higher response odds than waiting list, but limited evidence quality and publication bias prevented confirmation of these differences.

Abstract

Objective Various control conditions have been employed in psychotherapy trials, but there is growing suspicion that they may lead to different effect size estimates. The present study aims to examine the differences among control conditions including waiting list ( WL ), no treatment ( NT ) and psychological placebo ( PP ). Method We comprehensively searched for all randomized controlled trials ( RCT s) comparing cognitive‐behaviour therapies ( CBT ) against various control conditions in the acute phase treatment of depression, and applied network meta‐analysis (NMA) to combine all direct and indirect comparisons among the treatment and control arms. Results We identified 49 RCT s (2730 participants) comparing WL , NT , PP and CBT . This network of evidence was consistent, and the effect size estimates for CBT were substantively different depending on the control condition. The odds ratio of response for NT over WL was statistically significant at 2.9 (95% CI : 1.3–5.7). However, the quality of evidence, including publication bias, was less than ideal and none of the preplanned sensitivity analyses limiting to high‐quality studies could be conducted, while findings of significant differences did not persist in post hoc sensitivity analyses trying to adjust for publication bias. Conclusion There may be important differences in control conditions currently used in psychotherapy trials.