ARS Technica’s John Timmons considers the research of Christopher A. Parsons, Johan Sulaeman, Michael C. Yates and Daniel S. Hamermesh, and their June 2011 study, “Strike Three: Discrimination, Incentives, and Evaluation”.  In their published report, the quartet compared the racial backgrounds of MLB pitchers and umpires to try and determine whether or not the ethnicity of one might impact the calls of the latter.  Their findings?  In Timmons’ summation, “a subtle bias that went away when the umpires thought someone was watching them,”, that someone being QuesTec.

In its simplest form, when an umpire was from the same ethnic group as the pitcher, they were more likely to call a pitch a strike, at least at a ball park that was not equipped with a QuesTec monitor. When the same analysis was performed at a QuesTec game, the probability that a pitch would be called a strike when there was matching pitcher/ump ethnicity dropped by a full percent—”more than offsetting the favoritism shown by umpires when QuesTec does not monitor them.” This was specific to pitchers, as running the same analysis with the catcher and the batter showed no statistically significant differences.

It wasn’t just the presence of the automated system, though, as the authors found that any situation that would lead to heightened attention on the umpire changed the ball/strike calls. These included having more fans in the stands, and pitches that were more likely to be decisive (the pitcher had thrown three balls or two strikes, meaning the next pitch could end the at-bat). Most of the effects were very small, but the authors note that, in rare edge cases, they could add up. “One can construct specific examples where the estimated direct effect is fairly large,” they write. “A black pitcher throwing a nonterminal pitch in the early innings of poorly attended games in a non-QuesTec ballpark gains over 6 percentage points by matching [the umpire’s ethnicity] (41.4 versus 35.2 percent called strikes).”

There were some variations in the numbers; for example, minority pitchers tend to have fewer pitches called as strikes even by umpires from the same ethnic group, and this effect is actually enhanced by QuesTec monitoring. And white umpires tended to call balls and strikes for minority pitchers about equally regardless of whether they were monitored—but this rate was about a full percentage below the number of strikes they called for white pitchers.

One interesting effect suggests that this bias might either go away with experience, or that major league baseball was aware of it on some level: the 18 most senior umpires that act as crew chiefs showed no indication of bias.