The Iron Curtain and Referee Bias in International Football

Using the assignment of referees to European international association football matches played between 2002 and 2016, we ask whether judgments were biased according to the legacy of the Cold War. We find that referees from post-communist states favored teams from non-communist states, but there was no evidence of favoritism in the other direction. This out-group bias of referees born behind the Iron Curtain was statistically significant for relatively less important and more subjective decisions, namely the awarding of yellow cards for foul play. The bias was particularly large among referees from the former Soviet Union. It has also diminished over time, perhaps due to increased professionalism in European refereeing, or because memories of the Cold War era have diminished among active referees.