Relative age effect in Mexican professional and youth soccer

In youth football, categories are defined by the players’ year of birth. In one category, there can be an age difference of almost 12 months, which may manifest itself in considerable physical differences. The impact of this "relative age" is reflected in elite teams by an overrepresentation of players born in the first months of the year, called "Relative Age Effect" (RAE). In the present study, this bias was analyzed among the 4499 Mexican players (3531 men, 968 women), registered by the 18 professional clubs for the 2022 season in men’s First Division, their U20, U18, U17, U16, U14 categories, women's First Division, and their U17 categories. From every player were collected: birthday, playing position, minutes played for their teams, and their teams’ final rank in the National Championships. In all categories, except women's First Division, a statistically significant RAE was found, whose size was greater in the lower categories than in the major ones. The playing positions that presented a higher size of RAE were not the same in the different categories. A positive correlation was found between RAE and individual and team performances. These results indicate the need to take a deeper look at the selection and development processes of talented players in Mexico, because players initially favored by their greater relative age do not reach the professional soccer teams in the same proportion.