Monday, July 30, 2012
Breaking FIP
This blogger points out that Chapman’s FIP for the month of July is negative.
Since FIP is a linear equation that tries to model linearly what is non-linear and inter-dependent, by definition that makes FIP an approximation. And approximations break at some point. The best approximators break as little as possible, in extreme situations, fairly easy to identify. When you get 2 strikeouts per inning, that’s what happens.
FIP was always intended as a quick way of getting to the answer that the complex DIPS-based process would get to. What was opaque, but valid, with Voros’ method was made transparent by the FIP process. When you achieve r=.90-.98 with a simple transparent approximation, that’s considered a resounding success.
Since r is not equal to 1, that means that, sometimes, things aren’t captured well. And in rare instances, the approximation is just giving the wrong answer. And that’s what happened here.
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