INTRODUCTION: The relative age effect (RAE) is a well-known phenomenon that has been observed in many sports. In this context, elite level football is amongst the fields of interest that have been studied frequently (Deprez et al., 2013). Thus, the level of competition is one of the factors affecting the RAE. Earlier studies showed that the RAE is more pronounced in higher competition levels, which is explained by an increase in selection pressure (Jackson & Comber, 2020). At the same time, elite academies have access to higher qualified coaches and extensive scientific resources regarding the selection of talents. For this reason, one would expect weaker RAE at elite level. To gain further sport specific insight, this study aims to compare the prevalence and magnitude of the RAE between elite and sub-elite level in youth football. METHODS: A total number of 1.728 football players from age groups U10 to U19 representing a certified academy of a professional club of German Bundesliga (n=876) and a cohortof a sub-elite club of German 4th division (n=852), respectively, for subsequent seasons between 2015/16 - 2020/21 served as data pool. Birth dates were collected, differences between the observed and expected birthdate distributions were analysed using chi-square and Cramer`s V was used to estimate the magnitude of effect sizes according to age groups. RESULTS: The findings reveal birthday asymmetry in both elite and sub-elite cohorts, with a greater extent in elite level (e.g. 1st half year U10:73.4% in elite versus 64.4% in sub-elite). While elite level players show a consistent significant RAE across all age groups (each p<0.05) with medium to large effect sizes, there is no RAE for age groups U10 to U15 in sub-elite level found (each p>0.05). However, there is a significant RAE in U17 (p<0.05) and U19 (p<0.05) with medium effect sizes in sub-elite level. CONCLUSION: The findings confirm earlier results of consistent prevalence and magnitude of RAE in youth elite football players. The comparison shows that the effect is much more pronounced in elite level than in sub-elite level, supporting the line of argumentation that selection pressure has a strong impact on the magnitude of RAE. Further studies including additional factors (e.g. maturation, physical and psychological dimensions) are needed to gain more insights on this phenomenon.
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