A historical examination of relative age effects in Major League Baseball

Bolun Zhang *, Srdjan Lemez **, Nick Wattie *** and Joseph Baker *

(*) School of Kinesiology and Health Science, York University, Toronto Canada
(**) School of Kinesiology and Nutritional Science, California State University, Los Angeles USA
(***) Nick Wattie, Faculty of Health Sciences, University of Ontario Institute of Technology, Ottawa Canada


Zhang, B., Lemez, S., Wattie, N., Baker, J. (2018). A historical examination of relative age effects in Major League Baseball. International Journal of Sport Psychology, 49(5), 448-463. doi:10.7352/IJSP.2018.49.448


This study examined the emergence and existence of relative age effects (RAEs) among American-born Major League Baseball (MLB) players participating between the 1871 and 2014 seasons (N = 16,122). This study also investigated a range of possible moderators of these effects (i.e., handedness, position, career length, and debut age). Overall, a significant RAE was found for players born between 1950 and 1970, with small RAEs (effect sizes ranging from .112 to .207) more common in pitchers (1950s-1970s) and right-handed throwing players (1960s and 1970s). Relative age did not appear to influence players’ career length; however, a significant difference in debut age was found between birth quartiles. Overall, this longitudinal examination provides unique evidence about the occurrence and persistence of RAEs over the history of MLB.

Keywords: Career length, Debut age, Handedness, Position