Different control conditions can produce different effect estimates in psychotherapy trials for depression

Objectives: Control conditions' influence on effect estimates of active psychotherapeutic interventions for depression has not been fully elucidated. We used network meta-analysis to estimate the differences between control conditions.

Study design and setting: We have conducted a comprehensive literature search of randomized trials of psychotherapies for adults with depression up to January 1, 2019 in four major databases (PubMed, PsycINFO, Embase, and Cochrane). The network meta-analysis included broadly conceived cognitive behavior therapies in comparison with the following control conditions: Waiting List (WL), No Treatment (NT), Pill Placebo (PillPlacebo), Psychological Placebo (PsycholPlacebo).

Results: 123 studies with 12,596 participants were included. The I-squared was 55.9% (95% CI: 45.9%; to 64.0%) (moderate heterogeneity). The design-by-treatment global test of inconsistency was not significant (P = 0.44). Different control conditions led to different estimates of efficacy for the same intervention. WL appears to be the weakest control (odds ratio of response against NT = 1.93 (1.30 to 2.86), PsycholPlacebo = 2.03 (1.21 to 3.39), and PillPlacebo = 2.66 (1.45 to 4.89), respectively).

Conclusions: Different control conditions produce different effect estimates in psychotherapy randomized controlled trials for depression. WL was the weakest, followed by NT, PsycholPlacebo, and PillPlacebo in this order. When conducting meta-analyses of psychotherapy trials, different control conditions should not be lumped into a single group.