Supplementary Material for: Intensity of Treatment as Usual and Its Impact on the Effects of Face-to-Face and Internet-Based Psychotherapy for Depression: A Preregistered Meta-Analysis of Randomized Controlled Trials

<b><i>Introduction:</i></b> Treatment as usual (TAU) is the most frequently used control group in randomized trials of psychotherapy for depression. Concerns have been raised that the heterogeneity of treatments in TAU leads to biased estimates of psychotherapy efficacy and to an unclear difference between TAU and control groups like waiting list (WL). <b><i>Objective:</i></b> We investigated the impact of control group intensity (i.e., amount and degree to which elements of common depression treatments are provided) on the effects of face-to-face and internet-based psychotherapy for depression. <b><i>Methods:</i></b> We conducted a preregistered meta-analysis (www.osf.io/4mzyd). We included trials comparing psychotherapy with TAU or WL in patients with symptoms of unipolar depression. Six indicators were used to assess control group intensity. Primary outcome: Standardized mean difference (SMD) of psychotherapy and control in depressive symptoms at treatment termination. <b><i>Results:</i></b> We included 89 trials randomizing 14,474 patients to 113 psychotherapy conditions and 89 control groups (TAU in 42 trials, WL in 47 trials). Control group intensity predicted trial results in preregistered (one-sided <i>p</i>s &lt; 0.042) and exploratory analyses. Psychotherapy effects were significantly smaller (one-sided <i>p</i> = 0.002) in trials with higher intensity TAU (SMD = 0.324, CI 0.209 to 0.439) than in trials with lower intensity TAU (SMD = 0.628, CI 0.455 to 0.801). Psychotherapy effects against lower intensity TAU did not differ from effects against WL (two-sided <i>p</i> = 0.663). <b><i>Conclusions:</i></b> Our results suggest that variation in TAU intensity impacts the outcome of trials. More scrutiny in the design of control groups for clinical trials is recommended.