Temporal trends in the relative age effect in five major European men’s football leagues, 2000–2025

< .001; Cramér's V = 0.085). The same pattern was observed in the unique-player analysis (V = 0.085), suggesting that the pooled distribution was not driven solely by repeated seasonal observations of the same players. Season-level estimates increased during the earlier part of the observation window and subsequently stabilised, rather than showing continuous linear amplification across the full 25-season period. This temporal pattern varied substantially by league and requires interpretation in light of cohort replacement, player mobility, developmental-cutoff uncertainty, and changing league composition.