The Favourite’s Advantage: Evidence of Referee Bias in European Football

This study examines how favoritism influences professional decision-making in high-pressure environments where impartiality is crucial. Using professional football as a laboratory, we leverage novel data that precisely measure discretionary decisions made by highly trained officials. Analyzing over 7,000 decisions across five major European football leagues, we find systematic bias favoring stronger teams that increase with quality disparity and is most pronounced when decisions are highly consequential. These findings contribute to our understanding of favoritism in professional judgment, particularly where discretionary power coincides with quality differences between participants.