Monday, May 07, 2012
Ross Detwiler: Losing to the statistical gods
This was a mailbag question from nearly two years ago (Aug 26, 2010):
I noticed that Ross Detwiler has never had a HR/FB% over 6% in any of his stints in his professional career. In his last 6 stops, he has had a 4% HR/FB% or less in all of them. By my math, that is about 19 HR allowed in 552 estimated Flyballs which comes out to a 3.44 HR/FB%. Let’s say I was off a little and his HR/FB% is really 4%. Can we say that he has a skill for reducing his HR/FB% rate. Or is it a fluke based off his sample size (Around 500 professional innings)?
At the same time, Detwiler has allowed a BABIP over .323 in every stint in his career except for 1 4 Inning fall league appearance. He’s ranged from .323 to .378 in BABIP. By my math that might be slightly off, his BABIP in his career is about .345. It looks like his GB% is normal (Around 45-50%). Do you have any reason why his BABIP is so high consistently. In his short big league career he has a 24.8 LD% (89.2 IP). Assuming he is around that in the minors, does that even close to explain his abnormal BABIP. Does he have a skill for real high BABIP? And is there some kind of link between his real low HR/FB% and his real high BABIP?
Sure enough, in 2011, his BABIP was .272, and in this early 2012, he’s at .215. So, the reader seems to think he sees a “pattern” of a high BABIP, but the sample size gods were not kind to the reader. As for his ability to suppress HR, in 2011+2012, he’s given up 9 HR on 92 FB, which is right around league average. Sample size gods are not nice.
I get these kinds of emails all the time, that someone thinks they found THE fluke guy. But, it’s the same thing every time. Seriously, if you really think you know more than the sample size gods, then pick out the twenty things you really believe more than everyone else, write it down, and then two years from now, tell me how you hit on 15 of 20. (Of course, if enough people do this, SOMEONE is going to hit on 15 of 20 due to the binomial gods of random variation.)
My suggestion: stop looking at numbers looking for patterns and building narratives in your mind, and instead enjoy the numbers for the actual stories they tell. Meaningless stories, stories that don’t carry over to the next day.
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