Relative Age Effect in Judo Competitions: Influence of Age, Weight Category, Sex, and Time Frames

This study was conducted to determine whether the relative age effect (RAE) is present in different age groups, weight categories, sexes, and across different time frames in international-level judo competition. A total of 9451 judo athletes competing at the Olympic Games and/or World Championships in the Cadet, Junior and/or Senior age groups between 1993 and 2020 were considered. Athletes' birthdate distributions were grouped in four quartiles (Q1: January-March; Q2: April-June; Q3: July-September; Q4: October-December) and compared to a day-corrected theoretical distribution using Chi-squared analysis. Poisson regression was also used to evaluate the ability to explain weekly birth count. RAE was more prevalent in males than females (p < .05), and for Cadets and Juniors compared to Seniors (p < .05). Heavyweight and middleweight categories presented RAEs in Senior and Junior males, while for females it was present in Cadet heavyweights (p < .05). RAE was more prevalent in recent years (2009-2021) for Senior male judo athletes (p < .05). Poisson analysis illustrated some nuanced information, including RAE detection during an earlier time frame, not readily apparent with the traditional analysis.