Background/Purpose Relative age effects have been found in many sports. Individuals who are born in the early months of age-grouped sport competition are more likely to reach professional sport. Grondin and Koren (2000) reported significant relative age effects for right handed major league pitchers born after 1960, but no relative age effects for left handed pitchers or non-pitchers. The purpose of this study was to determine if relative age effects are present in minor league players at the AAA and Rookie league level. Methods Data for AAA and Rookie league players on the 2012 rosters (player position, handedness, birth date) were obtained from www.BaseballAmerica.com. Players birth dates were classified into four quadrants based upon the initiation date, August 1, for age grouped competition in baseball (August, September, October, quadrant 1, etc.)
Analysis/Results Chi Square analyses were conducted to determine the probability of players exhibiting a higher proportion of players being born in the early quadrants. A significant relative age effect was found for left-handed pitchers in the AAA leagues and for right handed pitchers in the Rookie league. Sixty-three percent of AAA left-handed pitchers and 57% of right handed Rookie pitchers were born in the first and second quadrants. No relative age effects were found for other players.
Conclusions Comparisons with other studies suggests relative age effects are smaller for professional baseball players in comparison with other sports (soccer, ice hockey) and may be limited to pitchers. Further research is needed to determine the underlying causes of relative age effects.