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August 15, 2012

Manufactured Runs

The Importance of Imperfect Models

by Colin Wyers

From the Twitters yesterday morning:

All the context you really need to know to understand that tweet:

• He’s referring to the implementation of WAR on Baseball-Reference, and
• The fielding metric currently in use there, DRS, has Barney’s defense rated at over twice what any other popular fielding metric does.

I leave the matter of Barney’s defensive rating as an exercise for the reader—that equine hasn’t stopped twitching, but I’ll hold off on the beatings for right now. No, I want to discuss something that came out of a long discussion on Twitter in response to that remark: What does it mean when we think WAR (or any other metric) is wrong? Can we still use it? Should we discard it until we’ve worked out all the imperfections?

Or another example – CBS Sports recently ran a piece entitled “Aroldis Chapman broke FIP.” The heart of the piece:

So, that's the short version -- and here's the fun outlier, Chapman's FIP for July is -0.99 -- that's right, that little mark in front of what would be an impressive FIP means it's silly good. (His xFIP is a slightly less -- but still completely certifiable -- crazy -0.73.)

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