We investigate the racial preferences of Major League Baseball umpires as they evaluate both pitchers and hitters over approximately 25 million pitches from 1989-2010, including the 2002-2006 period in which "QuesTec" electronic monitoring systems were installed in some ball parks. We find limited, and sometimes contradictory, evidence that umpires unduly favor or unjustly discriminate against players based on their race.
Variables including attendance, terminal pitch, the absolute score differential, and the presence of monitoring systems do not consistently interact with umpire/pitcher and umpire/hitter racial combinations. Most evidence that would first appear to support racially-connected behaviors by umpires vanishes in three-way interaction models. Overall, in contrast with some other literature on this subject, our findings fall well short of convincing evidence for racial bias.
This is joint work with John Rasp at Stetson University.