Tuesday, October 07, 2008

Do power pitchers have an advantage in the post-season?

Yesterday, Bill James, over at his website (subscription required), ran a matched-pair study to see if power pitchers do better in the post-season than control (finesse) pitchers. He finds that they do. Given equal W-L records, starts, and runs saved, the strikeout pitchers wind up outperforming the control pitchers, by a fairly significant amount.

In response,
Tango argues that Bill's method doesn't properly match the pitchers, because, even though they have appear to have similar records and careers in all respects other than Ks and BBs, the study didn't control for BABIP (batting average allowed on balls in play). To match the power pitchers in ERA, the control pitchers would have had to have had a better BABIP. And, given that a good BABIP is mostly luck, that would explain why the control pitchers did worse in the playoffs – their luck just went back to normal.

I agree with Tango's analysis (and with mgl, who is critical of the study in the comments to Tango's post).

Another way to put it is that Bill's study is legitimate – it truly does find that, all else being equal, power pitchers do indeed outperform control pitchers in October. But the reason they do so is simply that for a control pitcher to have the same regular-season record as a power pitcher, he has to have been lucky with respect to balls in play. And the luck doesn't carry forward into the future.

Twenty years ago, Bill's conclusion would have been valuable to bettors and GMs – it would have told us something new. But, in today's world, sophisticated sabermetricians are already controlling for balls-in-play luck. So, in this case, Bill's study just gives us another confirmation of what we already know about predicting pitcher performance.



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