Chipper Update

This is getting interesting. Hitting .420 on June 8 is a whole lot different than hitting .400 on May 11.

The most difficult part of figuring out Chipper's odds of hitting .400 is figuring out his true batting average. The five projections listed at FanGraphs had his 2008 BA anywhere between .294 and .318. Figuring in 260 PAs of a .420 BA, that means something between .320 and .339 the rest of the year. The odds of a .320 hitter hitting .400 over 400 ABs are 1 in 2000; the odds for a .339 hitter are 1 in 161. So which true BA to use is a very important decision.

The best solution I can come up with is to use a whole bunch of projections. From now on, I'll be using four-- PECOTA, ZiPS, Marcel, and CHONE. Here are his preseason BAs according to each, as well as what we should expect from him the rest of the year.


So each of those will be weighted 25%. The next thing to figure out is how many at bats he'll end up with. This is also very important, and can't simply be done by finding an average. The following calculations are, admittedly, extremely rough, but here's what I used:

These average out to around 615, but you have to run each situation separately. For example, if there was a 50% chance a .300 hitter got 1 AB, and a 50% chance he got 999, you couldn't run one simulation with him getting 500 ABs to figure out his chances of hitting .400 over the sample; you'd get an absurdly low estimate.

Combining the batting average and playing time estimates, we get 28 difference scenarios. Here is the chance that each scenario has of him hitting .400:

Unsurprisingly, there is a huge spread here. Using CHONE and 691 PAs, the odds of Chipper hitting .400 are 1 in 192; using ZiPS and 520 PAs, they're better than 1 in 10.

Combining all of these, and weighting each playing time scenario as specified above, we arrive at 3.61%, or about 1 in 28. Because of the issue explained at the bottom of this post, that's a little conservative. It's hard to know exactly how much, but I'd say Chipper's true odds of hitting .400 are about 1 in 25. Certainly a far cry from the 1 in 546 odds of a month ago.

Photo: Braves Beat.