The relative age effect in a professional football club setting |
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Authors: | I?igo Mujika Stijn PJ Matthys Juanma Santisteban Juan Goiriena Renaat Philippaerts |
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Affiliation: | 1. USP Araba Sport Clinic, Vitoria-Gasteiz , Basque, Country, Spain;2. Department of Physiology, Faculty of Medicine and Odontology , University of The Basque Country , Bilbao, Spain;3. Department of Movement and Sports Sciences, Faculty of Medicine and Health Sciences , Ghent University , Ghent, Belgium;4. Medical Services , Athletic Club Bilbao , Bilbao, Spain;5. Department of Physiology, Faculty of Medicine and Odontology , University of The Basque Country , Bilbao, Spain |
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Abstract: | Abstract The relative age effect is an uneven distribution of birth date favouring subjects born in the initial months of a selection year. This study compared the birth-date distributions between several subgroups of Basque football players to identify whether the relative age effect is influenced by age and/or skill level. The study comprised 13,519 players including 114 senior professionals from the Spanish league's AC Bilbao over 21 seasons; over the season 2005–2006, it comprised elite youth (n = 189) from the same club's academy; regional youth (n = 4382) U11–U14 locally federated players; school youth (n = 8834) U10–U11 locally registered school district players. Differences between the observed and expected birth-date distributions were tested based on data from the general Basque male population. Significant chi-square values were followed up by calculating odds ratios and 95% confidence intervals (CI) for the quartile and half-year distributions to examine subgroup differences in the relative age effect. Birth-date distributions of all groups of players showed a significant bias towards early birth in the selection year compared with the reference population (senior, χ2 3 = 24.4, P < 0.001; elite youth, χ2 3 = 59.1, P < 0.001; regional youth, χ2 3 = 41.4, P < 0.001; school youth, χ2 3 = 40.9, P < 0.001). Between-group comparison revealed that the relative age effect incidence progressively increased with a higher level of involvement in youth football. This bias represents a significant loss of potential youth football talent. |
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Keywords: | Birth-date maturation talent identification talent selection youth development |
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