An international study of human handedness: the data.

Human handedness has been the subject of systematic study since 1646, but there is no agreement among researchers as to who can be considered a left-hander, what is the etiology of left-handedness, or what the proportion of left-handedness is in the world's population. This article reports the results of a handedness survey administered to 12,000 subjects in 17 countries, the largest handedness survey attempted. The paper discusses methods for determining handedness, the probability of a genetic component for handedness, and the relationship of sex, birth order, multiple birth, and first-degree relative's handedness on subject's handedness. A hypothesis for the etiology of left-handedness is presented.