Researchers say they can't determine if the bias is a result of a conscious or subconscious decisons.
Sabermetrics fans will love this.
A study released last month by Southern Methodist University makes the argument that racial discrimination between umpires and pitchers in Major League Baseball lowers the performance of minority pitchers, and their salary.
One of the study's authors, SMU assistant professor of finance Johan Sulaeman, said the research group used 3.5 million observations, or pitches, between 2004 and 2008 to determine if there is a bias against minority pitchers by white umpires.
The study compares the game called by the umpires against the results of video evidence recorded by MLB to illuminate the bias.
"We look at pitch-by-pitch information. For each pitch, we know what happened to the pitch. Is it a ball? Is it a strike? Is it a swinging strike? Is it a called strike?" Sulaeman said. "For some parts of the analysis, we also look at the location of the pitch using the technology that's now available ... so if you watch a game you can see whether the ball's in the strike zone."
According to researchers, the study revealed that strikes are called less frequently if an umpire and pitcher are of different races, but only in cases where games aren't monitored by cameras that record pitches and their location -- a common practice today in the MLB to ensure effective umpiring.
It further indicates that if minority pitchers are aware of the bias, and if the umpire is of a different race, the pitchers may throw more pitches over the middle of the plate since they don't think they'll get the strike call near the outside of the zone. Conversely, if white pitchers are aware of the bias, they may throw more to the edges rather than in the middle of the plate anticipating a more forgiving strike zone from a white umpire.
The study alleges that the bias creates a lack of productivity for the minority pitcher who tries to throw safer strikes in a smaller strike zone while it creates an increased level of productivity for a white pitcher who enjoys a wider, more forgiving strike zone. In both cases, wages may be affected as one pitcher is perceived to throw more strikes than the other and, therefore, unfairly judged to be a better pitcher.
"In all likelihood, this bias is subconscious and that's why, when they're [the umpires] being monitored, they don't show the bias anymore. If the performance measures [strikes vs. balls] are biased then we can see wage discrimination without realizing that it's there, because we're gonna say, 'Well, the minority pitchers are worse, that's why they're getting paid less.' That's not true, because, now the performance measures themselves are biased," Sulaeman said. "Even if we do interview the umpires, there's no way that we can figure it out."
After all, what umpire would admit to giving pitchers who share his race a more favorable strike zone?
Either way, those days are gone. The use of cameras to make umpires more accountable has been in use in every major league park since Opening Day 2009. According to the data, accountability removes the bias.
NBC 5's Justin Hinton contributed to this report.