Fun with Translation: BABIP
As some of you know, trying to translate minor league performance is one of my passions in baseball analysis, and not just for the motive of improving my projections (I’ve been working with them since the 1990s). I’ve tinkered with a lot of the original MLE formula of James (as have Davenport and Smith and others) and I’m now working one of my pet projects - working on BABIP and SLGIP for minor league hitters. We had a bit of a discussion about this in one of the Lidge trade threads, when talking about Mike Costanzo. I’ve theorized that one of the troubles with translating high strikeout batters is only indirectly a strikeout issue, but more likely a BIP issue, that high strikeout totals and success means a player generally has an unsustainable BABIP. So I had extra time this holiday weekend, being that it rained non-stop and I ducked family and I sure as hell wasn’t going shopping anywhere. Using data going back to 1992, thanks to Sean now having the data up handily, I found a few interesting things that look like they’ll improve my minor league translations.
First, it really looks like figuring out the number of balls hit into the field of play and the rate at which good things happen to those balls hit into player. Instead of a conversion rate for hits and the like, I’m getting more predictive results by finding the conversion rates for BABIP and finding the conversion rates for % of balls into play with a certain result. Pretty typically, a batter loses between 4 and 6% of their BABIP going from AAA to the majors, 3-5% from AA to AAA and less for lower level promotions. The change is small, but looking at my group of matched sets of low and high strikeout batters, it’s enough to eliminate the difference in projectability.
Just to use Mike Costanzo as the base (with 157 strikeouts), here are my MLEs for him with varying numbers of strikeouts:
OK, hardly a huge change, but we’re at the point with this particular stuff at which most of our changes to various concepts are going to be minor. Not sure if someone else has taken a look at this before and it would hardly be the first time I replicated work already done (Chone and I both spent a helluva lot of time in September making a rough translation of minor league defensive numbers to a rudimentary zone rating without knowing each other were doing it), but I thought I’d put it up just in case someone was interested.
My next project this winter? Looking back on the last 15 years not an eye on minor league—>major league numbers but an estimate of minor league projection—->major league numbers. I’m kinda wondering if a Marcel-type look at play in the minors instead of seasonal lines might wring out a little bit of noise.
Posted: November 27, 2007 at 07:15 AM | 33 comment(s)
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