Relation of handedness with season of birth of professional baseball players revisited.

We reexamined the relationship between month and season of birth and handedness in male professional baseball players listed in Lahman's Baseball Archive Vol. 4.5 database. The sample of 8,016 individuals (left-handed = 1,658; right-handed = 6,358) played major league baseball between 1900-2001. A slightly higher, but statistically significant, percentage of left-handed players were born in June compared to other months, and in the winter-spring months, but we were unable to corroborate Rogerson's spring and early summer categorization of handedness as related to birth season. The data did not support the hypothesis that the prevalence of left-handedness is related to season of birth.