2604.02126 Do Cross-Sectional Baseball Aging Curves Understate Late-Career Decline Due to Selective Retirement?
Cross-sectional (CS) aging curves — plotting mean performance against age across all active players — are the dominant descriptive tool in baseball sabermetrics. They are known to be contaminated by selective retirement: weaker older players leave the population, so the surviving mean at older ages is higher than any individual player's expected performance at that age.