Evaluators display significant in-group bias in many contexts. This paper shows that evaluators are less biased in the presence of a neutral colleague. We compile data on all international cricket since 1893, and analyse a series of reforms that introduced neutral umpires in international cricket matches. We present four results. First, prior to the reforms, both on-field umpires shared the nationality of the home team and make 9pp more discretionary calls against the foreign team. Requiring one of the two on-field umpires to be from a neutral country eliminates this bias. Second, half of this bias reduction is due to home umpires being less partial toward their team when paired with a neutral umpire. The de-biasing effects of neutral umpires are largest when an experienced neutral umpire is paired with an inexperienced home umpire. Third, we find, consistent with this, that a further reform requiring both on-field umpires to be from a neutral country had no additional bias reduction effect. Fourth, a “career concerns” reform that introduced TV referees and match executives to monitor and assess on-field umpires has no effect on bias. Collectively, these results suggest that social pressure from colleagues can discipline discriminators.
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