Exploring inter-league parity in North America: the NBA anomaly

The relative standard deviation (RSD) measure of league parity is persistently higher for the National Basketball Association (NBA) than the other three major sports leagues in North America. This anomaly spans the last three decades and is not explained by differences in league distributions of revenue, payroll or local market characteristics, placing the standard model of the professional sports league in question. The argument that a short supply of tall players is one possible explanation, but we offer a more attractive explanation. With a much greater number of scoring attempts in each game, basketball reduces the influence of random outcomes in the number of points scored per game and also season winning percentage. Our simulations demonstrate that lesser parity in the NBA is inherent in the rules of the game so that inter-league comparisons must be interpreted carefully.