Aside from the odds-related aspect that Gordon Pine mentioned, Mike Nunamaker also adjusted the impact values in his studies for the field sizes of the races in his sample. However, I don't know how you could take a set of impact values calculated according to Quirin's definition, and recalculate them after-the-fact to fit either Pine's or Nunamaker's method, without knowing odds data and field sizes for each of the individual horses or races in the sample (which are often not available, short of starting from scratch with your own calculations from original past performances). To me, Quirin's method suits the purpose well enough, as long as a sufficient sample size is used.
The true strength of the impact value for a particular factor or set of factors (and the effect on individual winning probability) can only be calculated or considered in the context of how all the other horses in the race stack up with regard to the same factor(s).
Last edited by Overlay; 08-19-2007 at 04:16 PM.
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