*2.4. Statistical Analyses*

For the outcomes of interest, an assessment was performed on the pooled effect of the treatment with psilocybin in terms of weighted mean differences (WMD) between the change from pre- and post-treatment mean values of the intervention and control groups. WMD combine measures, where the mean, standard deviation (SD) and sample size are known. The weight given to each study (how much influence each study has on the overall results of the meta-analysis) is determined by the precision of its estimate of effect and corresponds to the inverse of the variance. Statistical data analysis was performed using the Comprehensive Meta-Analysis software (Version 2.0) [17]. Forest plots were generated to illustrate the study-specific effect sizes with a 95% confidence interval (CI). The statistic I <sup>2</sup> of Higgins was used as a measure of the inconsistency across the findings of the included studies. The scale of I2 has a range of 0 to 100% and values on the order of 25%, 50% and 75% are considered low, moderate, and high heterogeneity, respectively [18]. Subgroup analysis was performed on the primary outcomes, depending on the dose and on the follow-up time after psilocybin administration. Three different analyses were used to evaluate the potential impact of publication bias on the present meta-analysis—Funnel plots; Egger's regression test; Duval and Tweedie's Trim and Fill approach. The sensitivity analysis was also achieved by eliminating each study one at a time to evaluate the stability of the results.
