Sunday, July 24, 2011

Predicting Using Winning Percentages

I'm working on a journal article summarizing my recent findings, and I realized that I never tested a predictor based upon winning percentages.  This is an unfortunate oversight, because winning percentages is the easiest obvious measure of a team's strength, and was the primary metric for selecting (at-large) Tournament participants before the development of RPI.  And RPI was developed primarily to address the criticism that not all winning percentages are equal.  So I've corrected that error by going back and testing a predictor based upon winning percentages:

  Predictor    % Correct    MOV Error  
1-Bit62.6%14.17
Winning Percentages 65.0%11.63
RPI (infinite)74.6%11.33

Both results are interesting.  % Correct shows little improvement over simply picking the home team to win every game, which I take to be further confirmation of the HCA in college basketball.  On the other hand, MOV Error is nearly as good as the best variant of RPI.

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