Are Female Left-Handers Rare?

Research shows that men are more likely to be left-handed than women.

Posted Mar 30, 2019

About 90 percent of Americans are right-handed and only about 10 percent are left-handed. However, as early as in the 1940s (Rife, 1940) some researchers noticed a curious fact about left-handedness: Female left-handers seemed to be rarer than male left-handers. However, not all studies found this effect, and the difference in numbers between male and female left-handers varied substantially between different studies.

So are female left-handers really rarer than male left-handers, and to what extent? In 2008, a research team lead by Marietta Papadatou-Pastou conducted a meta-analysis to answer this question once and for all (Papadatou-Pastou et al., 2008). A meta-analysis integrates the results of several empirical studies, which has the advantage that the sample size is much larger, increasing statistical power and rendering the analysis less likely to be affected by sample characteristics of individual studies. Overall, 144 studies with a total sample size of 1,787,629 individual participants (831,537 men and 956,092 women) were included in the analysis.

So what did the researchers find? The results clearly demonstrated that there was a robust gender difference for handedness. The authors found that the male to female odds ratio was 1.23. This indicates that if females had a chance of being left-handed of exactly 10 percent, males would have a 12 percent chance (the exact percentages vary a bit depending on geographical region). Given the low incidence of left-handedness in general, this 2 percent increase is quite a substantial difference. Similar results were also reported by a recent study that investigated left-handedness in the UK Biobank study, a large dataset with about 500,000 participants (de Kovel et al., 2019). Here it was found that in the UK, 8.6 percent of women and 10.6 percent of men were left-handed. Since both of these studies had large samples, we can be confident that there is indeed a gender difference in handedness, with left-handed women being rarer than left-handed men.

Is there any explanation why this is the case? In fact, scientists have yet to find a causal proof for why female left-handers are rarer than male left-handers. Several ideas have been proposed, including both environmental and genetics factors. For example, women might face stronger societal pressure to write with the right hand, but it could also be due to influences of hormones on brain development, or direct effects of specific genes on the X chromosome. More research is needed before any final conclusions can be drawn.

References

de Kovel CGF, Carrión-Castillo A, Francks C. (2019). A large-scale population study of early life factors influencing left-handedness. Sci Rep, 9, 584.

Papadatou-Pastou M, Martin M, Munafò MR, Jones GV. (2008). Sex differences in left-handedness: a meta-analysis of 144 studies. Psychol Bull, 134, 677-699.

Rife DC. (1940). Handedness, with Special Reference to Twins. Genetics, 25, 178-186.