The authors say “less than one pitch per game,” but unless I’m misreading the paper the effect is more like one pitch every FIVE games. They conclude the called strike rate is .0034% higher when pitcher and umpire are same race. About one-half of pitches are called by the ump, so that means about one-quarter of a pitch per game. And comparing 100% to 0% same-race overstates the real effect, since no racial group of pitchers is at either extreme. Add it all up, and a white starting pitcher gains an advantage of perhaps half a run over an entire season.

I am a statistician and when I reached the “effect of the bias is very small” comment I rolled my eyes. A little less than a pitch a game is less than a 1% sway and cannot accurately be described as bias. The number of pitches observed in the study may reduce the margin of error below 1%, but the number of pitchers observed is not even close. A single pitcher, bad or good, out of maybe 500-600 observed over a three year time frame can create this small of an aberration. The fact that much more than half of the umpires and pitchers are white would locate most of this alleged bias between the two.

In my opinion, the researchers are misinterpreting the results of their study. There is, in fact, no bias.

and, if the post is correct, claiming evidence of bias is a little different than simply attributing causation, but you’re right in that no respectable social scientist would takea single study like this one and claim anything totally definitive

Basically, from what I know of evolutionary psychology, humans are hard wired to favor others in their racial or communal group which would suggest that there is probably some bias in all of us (and common observation would agree.) But, in this case, if the bias is so unconscious and the effect so small, I don’t see much purpose to it. You could just as easily spin it the opposite way–that despite human predililection for bias, the study shows that there is very little in baseball.