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Clutch Hits - Tango's 11 points to think about --- to understand why we regress towards the mean (February 12, 2004)
Discussion ThreadPosted 12:59 p.m.,
February 12, 2004
(#1) -
BirdWatcher
Tango, I admire your courage but question your judgement in reopening the regression to the mean can-of-worms !! Your 11 Commandments are fine, in so far as we are searching out a best estimate for a group, but as soon as we apply these principles to one specific individual, there are still some fundamental issues which the 2002 thread left unresolved - as summed up in "Late's" closing comment in that thread:
"I'm talking about understanding the true talent of the regulars, the guys who contribute to the game by accumulating 600-700 plate appearances for a number of seasons. I see no reason why their true talent is dependent upon the performance of others."
The bottom line is your methodology will always "drag down" a Barry Bonds and "drag up" a Rey Ordonez when there is no necessary reason why they shouldn't go in the other direction. Your Commandments simply don't address the issue of why, for these specific ball players, it is preferable to regress against the MLB "population" mean instead of their own career "sample" mean.
Even in the case of more limited sample sizes, for example, predicting performance for players entering their second full season who had 400+PAs in year one, why wouldn't you use as a population mean say, the average change in performance from year one to year two for all first year players in the last 10/20/30/40 years ?? Perhaps this is a better estimator then the overall MLB population mean, perhaps not. But, hey, let's talk about it (i.e selection of the population mean) each time we do one of these runs as opposed to treating the MLB population some sort of Aristotlean "truth."