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

Gabriele Morganti ¹ Adam Leigh Kelly ² Alexandra Lascu ^3,4 Paolo Riccardo Brustio ⁵ Elvira Padua ^1* Cristoforo Filetti ¹ Marco Porta ¹ Gianluca Briotti ¹ Bruno Ruscello ^1,6

• ¹ Università telematica San Raffaele, Rome, Lazio, Italy
• ² Birmingham City University, Birmingham, United Kingdom
• ³ Victoria University, Australia, Melbourne, Victoria, Australia
• ⁴ University of Canberra, Canberra, Australia
• ⁵ University of Turin, Turin, Piedmont, Italy
• ⁶ Department of Industrial Engineering, University of Rome Tor Vergata, Rome, Lazio, Italy

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 (n = 80) who competed in one of the five editions (2018, 2019, 2022, 2023, and 2024) of 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, by recording birth quarter (BQ) distribution of senior national team (n = 24) who competed at the 2024 UEFA Senior European Soccer Championship. Chi-square statistics revealed BQ1s were overrepresented at the U17 level (p < 0.001) and showed teams exhibiting low RAEs magnitudes recorded the highest likelihood (5.67) of finishing the tournament in the bottom four positions. Correlation analyses recorded small to moderate positive correlations between RAEs magnitude and population (.25) and FIFA points (.33). Further chi-square statistics revealed BQ1s continued to be overrepresented at the senior level, albeit with a weaker effect (p < 0.001). However, when the senior BQ distribution was compared to the expected distribution taken from the U17 population, this recorded more BQ4s and fewer BQ1s than expected (p < 0.001).Findings presented the focus on youth success and the competition for selection interact to reiterate RAEs' prevalence in soccer. Moreover, they highlighted initial RAEs define players' journey within the soccer system.