A Meta-Research of Randomized Controlled Trials in the Field of Mental Health: Comparing Pharmacological to Non-Pharmacological Interventions from 1955 to 2020.

Objective: This study aimed to provide a general overview of mental health randomized controlled trials (RCTs) and summarize the temporal trends in terms of the number of studies, median sample sizes, and median effect sizes using data collected from the Cochrane Database of Systematic Reviews (CDSR).

Methods: Using data collected from the CDSR, the temporal trends are compared in terms of the number of studies, median sample sizes, and median effect sizes between two broad categories of interventions: pharmacological RCT (ph-RCT) and non-pharmacological RCT (nph-RCT), and in conjunction with major mental disorder categories.

Results: Chronologically, the number of mental health RCTs reported in publications has increased exponentially from 1955 to 2020. While ph-RCT comprised a majority of mental health RCTs in the earlier years, the proportion of nph-RCTs increased more quickly over time and markedly exceeded ph-RCT after 2010. The median sample size for all 6,652 mental health RCTs was 61, with 61 for ph-RCT and 60 for nph-RCT. Over time, the median fluctuated but an increasing trend was observed over the past 60+ years. The median of the effect size, measured by Pearson's r, for overall RCTs was 0.18, and nph-RCT (0.19) had a larger median effect size compared to ph-RCT (0.16). Over the years, the nph-RCT had a larger median effect size than the ph-RCT. Differences in the median effect sizes among the categories of mental disorders were also noted. Schizophrenia had the most RCTs, with a median Pearson's r value of 0.17. Mood disorder had the second largest number of RCTs and a median Pearson's r value of 0.15. Neurotic/stress-related mental disorder had the third largest number of RCTs with the highest median Pearson's r being 0.23.

Conclusions: This study provides meaningful information and filled the knowledge gap in mental health RCTs.