RAE_2000-2025 — Data and Analysis Scripts: A Quarter-Century of Structural Selection Bias in Five Major European Football Leagues

This project examines the temporal trajectory of the relative age effect (RAE) in elite professional football over a 25-year period (2000–2025). The RAE refers to the systematic overrepresentation of athletes born early in the annual selection year, a bias that has been consistently documented across sports and competitive levels since the 1980s. The dataset comprises 60,078 player-season records (14,173 unique players) drawn from the five major European professional leagues — English Premier League, Spanish La Liga, German Bundesliga, Italian Serie A, and French Ligue 1 — across all complete domestic seasons from 2000–2001 to 2024–2025. Player birthdates were retrieved via Wikidata SPARQL and validated against FBref biographical records. Only players accumulating a minimum of 90 competitive minutes per season were included. The primary research question is whether the RAE has attenuated, stabilised, or intensified across a period during which it has been extensively documented and broadly communicated to practitioners. Analyses include: global birth quartile distributions; temporal trend modelling via OLS regression with Newey-West HAC-corrected standard errors (Durbin-Watson = 0.518); Spearman rank correlation; league-level and positional subgroup analyses; minutes-weighted indices; sensitivity analyses at three participation thresholds (≥90, ≥450, ≥900 min); Eurostat population-corrected baselines; unique-player robustness checks; and nationality-stratified analyses classifying players by developmental cutoff system. The central finding is that the RAE intensified systematically across the observation window (β = 0.00319/yr; HAC p < .001; Spearman ρ = .872), representing a marked increase in effect magnitude over 25 seasons, and that this amplification is robust across all analytical specifications. These findings provide longitudinal evidence consistent with the hypothesis that elite talent pipelines in professional football may not self-correct in response to scientific awareness alone.