Pearson’s correlation coefficients on the relation between study characteristics and study effect size (by meta-analysis indicated in the columns).

A The correlation between number of treatments and outcome was also present in studies that applied multiple treatments (r = .35 (202 data points) P Abbreviation. NA; Not Applicable.* Statistically significant at P ** statistically significant at P *** statistically significant at P NOTE. There was no evidence for between-study heterogeneity in the meta-analyses on serum BDNF levels. Correlational analyses therefore were not performed in this sub-group.Pearson’s correlation coefficients on the relation between study characteristics and study effect size (by meta-analysis indicated in the columns).