Relative age effects in European soccer: their association with contextual factors, impact on youth national teams' performance, and presence at the senior level.

Introduction: Soccer systems promote early identification and specialisation practices to satisfy short- and long-term goals-both from sporting performance and financial gains perspectives. In this context, players are (de)selected based on observed performance level and on their ability to conform to given organisational demands, leading to the proliferation of selection biases, such as relative age effects (RAEs), which research has shown to influence both developmental experiences and senior career achievements. Accordingly, this study aims to: (a) investigate the magnitude of RAEs among youth national teams competing in the UEFA U17 European Soccer Championship, and their associations with teams' final ranking, (b) examine whether RAEs magnitude could be linked to cultural and contextual factors, and (c) further explore RAEs at senior level. Methods: Birth quarter (BQ) distribution of youth national teams ( Results: Chi-square statistics revealed BQ1s were overrepresented at the U17 level ( Discussion: The findings presented the focus on youth success, the increased talent pool size, and the competition for selection interact to reiterate RAEs' prevalence in European soccer. Moreover, they highlighted initial RAEs define players' journey within the soccer system, whereby relatively older players remain overrepresented at the senior level, albeit to a weaker and lesser extent.