from Amazon
Wednesday, June 03, 2009
Joe Mauer
Walt Davis says:
Still, it’s over a 5-sigma variation which does suggest that this is a “process out of control” but all that tells us is that the “failure” rate (where each HR is a “failure") is higher than it used to be. The question then becomes what’s the new rate. It will be several hundred PA before we’ll have a good estimate of that but I’ll just point out that Adrian Gonzalez had 11 HR in May in 5 fewer PA so there’s no reason to think Mauer’s new level of talent is any higher than Gonzalez’s (who, to this point, has been a 25-35 HR guy though obviously he’s on a torrid pace right now).
And as always, I point folks towards Steve Dillard, Aug 2-17 1979—this sort of thing can happen “randomly.”
My response:
All Walt is suggesting is that the “out of control” performance is no longer from the same “true talent” as from the previous performance. BUT, the new estimate of the updated true talent will not be anywhere close to the “out of control” performance. That’s why he says he needs several hundred more PA.
Mauer in his career has 56 HR in 2514 PA, or 13 per 600 PA.
This year, he has 12 HR in 126 PA, or 57 per 600 PA.
Absent other information, from today to the end of the season, his HR rate will be far closer to 13 per 600 than 57 per 600.
How much though? This study from five years ago (post 2) suggests adding 131 PA of league average HR rate to your known information. So, if all we knew was the Mauer info of this year, his “true” HR rate would be about halfway between what he has hit (57 per 600) and what the league average is (16? per 600), or 36 or so per 600 PA.
However, for Mauer, we also have his past career, which shows him to not be a HR hitter. We can’t simply discard that information (unless of course we have some reason to believe that the Mauer of old approaches batting differently than the Mauer of new).
Just taking a WAG, if we consider the Mauer of old providing a good prior, that the Mauer of new is showing a strong indicator, and we always have our trusty friend regression toward the mean, my WAG is that Mauer will hit 25 per 600 PA from now to the end of the season.
Of course, being a binomial means that I’m 95% sure that it’s 25 per 600 PA, plus/minus 12 HR. Which basically means that whatever I say, or anyone says, insofar as Mauer is concerned, will be practically untestable.
It may be untesteable for the Mauer case, but couldn’t you test it for other similar cases in major league history? How about looking at a sample of players +/- 2 years of Mauer, looking at players +/- 3 HR/600PA close to Mauer, and then from that sample, look at any player that had huge HR numbers April/May ... and then check what they did from June to September.
come to think of it, isn’t this basically what PECOTA does, except it is from season to season and not an in-season study? If so, then maybe an easier and quicker study would be too look at players that jumped 10+ HRs in one season, and then see how well PECOTA’s predictions correlated with actual performance.