Fig. 4

Funnel plot of standard errors on logit prevalence. Funnel plots a “LH” (left-handedness), b “MH” (mixed-handedness), and c “NRH”(non-right-handedness) refer to meta-analysis set 1 (twins vs. singletons), and by means of a visual inspection no asymmetries could be identified. Funnel plots d “LH”, e “MH”, and f “NRH” refer to meta-analysis set 2 (DZ vs. MZ), and according to visual inspection we detected no asymmetries. Funnel plot g “concordance” refers to meta-analysis set 3 (concordance), and a visual inspection did not reveal any asymmetry