Skills vs. Luck: Decomposing Deviations from Expected Performance in European Football Leagues

Abstract

Statistics on expected goals and expected points in football provide insights into teams’ expected performance based on data about shots. Some teams exceed expectations, while others fall short of this benchmark. In this preregistered study, we employ random-effects meta-analysis to decompose the deviation from expected performance into luck and skills, using data from the top seven European football leagues for men over three seasons. Our results indicate that approximately 40% of the variation in over-/underperformance during a league season is attributable to skills, while the remaining 60% is due to luck. Over a season of 38 matches, these estimates imply that the standard deviations in points attributed to skills and luck are roughly 6 points and 7 points, respectively. We demonstrate the significance of luck through simulations, indicating that, on average, it affects league rankings by 1.8 positions and showing that luck plays a decisive role in determining end-of-season outcomes.