Saturday, June 07, 2008

Math Is Hard

David Pinto is now updating Chipper Jones's chances at hitting .400 this season.

To the layman, this might seem useful, but the results suffer from the ol' garbage-in-garbage-out problem. Pinto assumes that Chipper's "true" batting average is fixed at his career level of .310, which is absolutely ridiculous. Chipper has batted .348 since the start of 2006, and it's not like this number is some kind total fluke; his xBA from 2005-07 was .327. A more reasonable estimate of his true batting average for this season might be .335.

Furthermore, Pinto also assumes Chipper is a cardinal point and will never deviate from this level of ability. In reality, we know he could have an extremely healthy and productive year, or battle nagging injuries all the time. In other words, he is not going to be a true .335 hitter every single day of the year.

This is basically the same error made by pseudo-playoff odds projections like this one. Talent levels aren't fixed! Alert the media!

I personally think Chipper will finish the year above .400 about 5% of the time. But hey, if you believe David Pinto, Bookmaker.com will give you -2200 on the under, which is a steal for a 99.9% win rate.

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