Association of birthdate with success of nationally ranked junior tennis players in the United States.

The objective was to assess the effect of birthdate on successful performance in tennis by junior tennis players in the United States and to address the question of whether "birthdate effect" persisted with ongoing age toward adulthood. The national rankings and birthdates of junior tennis players in each age division were obtained from the United States Tennis Association. The number of male and female junior tennis players ranked within the top 100 in their respective age divisions with birthdates in the first half of the year were counted and compared with the number of junior athletes born in the second half of the year. A significant chi squared for birthdate by success in tennis was present in the 14 years and under and 16 years and under age divisions for boys. This effect was less for older ages. Among girls, the effect of birthdate on tennis ranking was not significant in any age group. Among male junior tennis players in the 14 years and under and 16 years and under age divisions, athletes born in the first half of the year had an advantage over those born in the second half, but not for girls.