Fig. 4
Forest plot of cross-sectional studies. J represents the number of outcomes. Black squares in the forest plot represent the meta-analytical study mean and the corresponding 95% confidence interval. Grey confidence intervals represent the sampling variance of observed effect sizes within each study and indicate the influence of the study sample mean on study precision. The thickness of the grey confidence intervals is proportional to the number of effect sizes within a study [66]. The numbers in parentheses designate the independent subsample within a study