The prevalence of left-handedness:Five meta-analyses of 200 studies totaling 2,396,170 individuals

Across time and place, right hand preference has been the norm, but is there a fixed prevalence of left- and right-handedness? Addressing this question is important for understanding individual differences within the general population, as well as furthering neuro-functional, neuro-anatomical, genetic, psychiatric, cognitive, and psychoendocrinological research, and for understanding the phylogenesis of Homo sapiens. However, agreement is still far from having been reached on the prevalence of left-handedness, as well as on the different factors that can affect its magnitude. We report five meta-analyses that summarize the vast field of handedness research and show that left-handedness prevalence lies between 7.9% (using the most stringent criterion of extreme left-handedness) to 15.4% (using the most lenient criterion of non-right-handedness), with the best overall estimate being 9.2% (9.0% when excluding studies assessing elite athletes’ handedness). Left-handedness prevalence is associated with (a) study characteristics, namely classification scheme, instrument, year of publication of the study, and purpose of the study, and (b) participant characteristics, namely sex, geographical ancestry, educational status, and sporting elite status. Moderators identified are highly relevant targets for future epigenetic studies on handedness and hemispheric asymmetries. We argue that the same evolutionary mechanisms should apply across geographical regions to maintain the 1:9 ratio, while cultural factors, such as pressure against left-hand use, moderate the magnitude of the prevalence of left-handedness. We urge researchers within the field of handedness to fully report study and participant characteristics, writing hand, Edinburgh Handedness Inventory scores, and make raw data publicly available