Relative age effect inverts when looking at career performance in elite youth academy soccer

The aim of this study was to investigate the well-known selection bias favouring players born earlier in the year commonly referred to as the Relative Age Effect (RAE). Therefore, we analysed a group of top-tier youth academy players. The players joined and left the youth academy at different stages, where the first stage was at 8 years (U9) and the last stage was at 18 years of age (U19). Subsequently, we followed the career paths of all players in terms of minutes played in professional competitions. For that purpose, we collected competition information from transfermarkt.de. We label a competition as professional if the included teams obtain an average market value of 100.000€ (aggregated value of players playing in the team) and recorded the professional career minutes (PCM) for all players. Results show that in the youth academy, there are fewer players that are born late in the year compared to players that are born early in the year, confirming previous findings of RAE. However, we also find that players that are born late in the year achieve more PCM on average. This indicates that players that survive the RAE selection bias are exceptionally good at achieving long, successful careers.