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Monday, May 05, 2008
Academics need to know about Angel Hernandez
Phil looks at what happens if you remove Angel Hernandez from a study:
If you take one of Laz Diaz and Angel Hernandez out of the sample of umpires, and replace him with an average umps, every statistically significant effect in the original Hamermesh study become statistically insignificant. And if you replace *both* of those two umpires, the effect not only becomes insignificant, but almost completely disappears.
But he also asks why single out Angel? After all, somebody has to be extreme. Let me be clear: I did not single him out because I looked at the data, and saw how far away he was. That’d be cherry picking. What I did do is point out that there are only 2 or 3 Hispanic umps, and Angel is notorious for his poor performance as an umpire. This is identical to saying that having a fat belly gives you great control, since I’ve only got two pitchers who weigh over 260lbs (CC and David Wells), and they are both lights out with the control. Might as well ascertain the bias to their bellies!
As one of Phil’s commenters said:
The problem, it seems to me, is that the unit of observation really isn’t the pitch, it’s the umpire. And with only two Hispanic and four black unpires in the study, it’s all but impossible to find out anything of significance--the standard erors at the level of the umpire are just going to be too large, and the required t-statistic for (conventional) statistical significance just too low. Until there’s a large enough sample of Hispanic and black umpires, what Hamermesh et al. have done cannot provide a test with enough power to allow us to reach a conclusion.
And that is exactly my point. How can you reach any kind of conclusion about racial bias, if you’ve got just two people that are part of that race?
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