When it comes to racism, the Reagan-era adage of “trust, but verify” seems apt, a new study finds.

A team of economic researchers examined three years of major league baseball games to determine if race played any role in officiating. They viewed more than 2.1 million pitches, noting the race or ethnicity of the pitcher and of the umpire pronouncing a strike or ball. They compared the overall pattern of calls made when pitcher and umpire were of the same race or ethnicity with ones made when pitcher and umpire were of different ethnic or racial backgrounds.

When pitcher and umpire were from the same ethnic or race group, the ump was more likely to rule in a pitcher’s favor, calling a strike rather than a ball, according to the still-unpublished study. The difference was just 1 percentage point but enough to influence pitchers’ stats and a few game outcomes.