There is a new working paper in economics available from the Institute for the Study of Labor which finds that when there is little outside scrutiny, umpires in major league baseball give preferential treatment to pitchers who share their race or ethnicity.

The paper, “Strike Three: Umpires’ Demand for Discrimination,” by Christopher Parsons et al., examines every pitch thrown in three recent seasons of major league baseball. The authors find that “pitchers who share the race/ethnicity of the home-plate umpire receive favorable treatment,” in the form of a higher probability of a pitch being called a strike rather than a ball.

Most interestingly, this effect only exists when the cost of exhibiting prejudice is low, that is, when the game is poorly attended, there is no computerized monitoring system which could detect the prejudice, or when the pitch is relatively unimportant in the game. This result holds up even when controlling for other factors which might be relevant, such as characteristics of the umpire, pitcher, or catcher.

The suggestion, of course, is that similar prejudice might be operating in other contexts, such as performance evaluation in employment. In this case, for instance, pitchers who are frequently evaluated by umpires of the same race or ethnicity will be recorded as striking out more batters, giving up fewer hits, and winning games more frequently.

The authors argue, moreover, that this phenomenon may affect research into employment discrimination. The reason is that any distortions in performance evaluation will cause discrimination in hiring, wages, or promotion to appear to be based on differences in employee quality or productivity.

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