Fig. 4

Methodological considerations for existing ML models towards psychiatric diagnosis. A illustrates increment trends for sample size during the recent three decades by Gaussian kernel density plots. Labeling 2011 sums up all the sample size from 1990 to 2011. B shows the counts for subgroups by dividing these studies according to sample size. C plots the trends of using cross-validation (CV) schemes by accounting counts from all the included studies during the recent three decades. D shows model performance comparisons between independent-sample validation and within-sample validation. The non-parametric W test was used for statistical inferences, with *** for p < .00. Precision-weighted accuracy was estimated by Woo et al. E depicts Gardner-Altman estimation for the classification accuracy comparison between population-within sample and population-across sample. Black dot indicated the point estimate for the mean difference (delta) of the two groups, and the shadow areas showed the distribution estimated by delta. F presents a frequency plot to show case–control skewness