Four meta-analyses across 164 studies on atypical footedness prevalence and its relation to handedness

Abstract

Human lateral preferences, such as handedness and footedness, have interested researchers for decades due to their pronounced asymmetries at the population level. While there are good estimates on the prevalence of handedness in the population, there is no large-scale estimation on the prevalence of footedness. Furthermore, the relationship between footedness and handedness still remains elusive. Here, we conducted meta-analyses with four different classification systems for footedness on 145,135 individuals across 164 studies including new data from the ALSPAC cohort. The study aimed to determine a reliable point estimate of footedness, to study the association between footedness and handedness, and to investigate moderating factors influencing footedness. We showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category. As many as 60.1% of left-handers were left-footed whereas only 3.2% of right-handers were left-footed. Males were 4.1% more often non-right-footed compared to females. Individuals with psychiatric and neurodevelopmental disorders exhibited a higher prevalence of non-right-footedness. Furthermore, the presence of mixed-footedness was higher in children compared to adults and left-footedness was increased in athletes compared to the general population. Finally, we showed that footedness is only marginally influenced by cultural and social factors, which play a crucial role in the determination of handedness. Overall, this study provides new and useful reference data for laterality research. Furthermore, the data suggest that footedness is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.

Figure 1

Flow diagram for search and inclusion criteria in the meta-analysis in accordance with the PRISMA guidelines for systematic reviews and meta-analyses. A complete list of studies included in the meta-analysis can be found in Supplementary Table S1.

Figure 2

Funnel plots of standard errors on logit prevalence (1), sex averages in point estimates (2), and handedness averages in point estimates (3) for non-right-footedness (A), left-footedness (L–R classification) (B), left-footedness (L-M-R classification) (C), and mixed-footedness (L-M-R classification) (D). The left-sided asymmetries in the funnel plots indicate that there were more studies with high error rates when the logit prevalence was below average indicating that small samples were imprecise in their estimates. Error bars represent the 95% CI. Please note that the nonR–R classification system contains data from all studies whereas the other graphs only contain data when it could be converted to the relevant classification system.

Figure 3

Forest plot for non-right-footedness grouped by sample type (control vs. clinical cohorts). The 95% confidence interval for each study is represented by a horizontal line and the point estimate is represented by a dot. The dashed lines and diamonds indicate the point estimates for the control (red) and the clinical (cyan) group.

Figure 4

Forest plot for left-footedness (L-M-R) grouped by sample type (general population vs. experienced athletes). The 95% confidence interval for each study is represented by a horizontal line and the point estimate is represented by a dot. The dashed lines and diamonds indicate the point estimates for each group.

Figure 5

Forest plot for non-right-footedness grouped by sample type (children vs. adults). The 95% confidence interval for each study is represented by a horizontal line and the point estimate is represented by a dot. The dashed lines and diamonds indicate the point estimates for each group.

Figure 6

Forest plot for mixed-footedness (L-M-R) grouped by instrument used to assess footedness. The 95% confidence interval for each study is represented by a horizontal line and the point estimate is represented by a dot. The dashed lines and diamonds indicate the point estimates for each group.