“Born to Play Ball” The Relative Age Effect and Major League Baseball

The records of 837 major league baseball players were examined in order to determine whether the Little League age eligibility criterion, based on the month of birth, affected participation rate at the professional level. The results indicated that major league players were more likely to have been born in the first months of the year, if that year corresponded to the one used for eligibility for Little League baseball (i.e., beginning in August and ending in July). A reanalysis of data presented in the literature (which suggested no effect) produced a similar result. These data are interpreted in terms of the relative age effect. That is, because of age cutoffs used in Little League baseball, some players gain a developmental advantage when competing against other youngsters who are considerably younger, although they are placed in the same age category for league play.