Fig. 3

Funnel plot of the meta-analysis. The standardized mean difference (SMD) on the x-axis is plotted against the standard error (SE) of the log(SMD) on the y-axis. A symmetrical distribution of studies indicates the absence of publication bias. An asymmetrical distribution with, for example, relatively more smaller studies with a positive result (in the lower right part of the plot) would suggest the presence of publication bias