## E-Rating Description

The E-Ratings were developed by
Eugene Potemkin, who maintains a complete
explanation
of his rating system.
As part of this web site, I calculate E-Ratings for many sports using the basic
ideas of Mr. Potemkin. Both the Buyer and Seller models are used. Instead of
subtracting (Rating = Seller - Buyer), I prefer to use a geometric average of
Seller and 1/Buyer (Rating = SQRT(Seller/Buyer)). The reason for this is that the E-Ratings are based on what is essentially an exponential model. Additional
adjustments are made to the algorithm in order to estimate the home advantage constant.

The essence of the resulting ratings is that the ratio of points scored
to points allowed can be determined. However, this is an awkward piece of
information. Instead we would like to be able to estimate the point spread
and the probability that one team would beat another.

I have devised an admittedly inelegant way to accomplish this
which won't be described here in detail. Since the E-Ratings are basicly
exponential, I first convert them to a linear scale by taking logarithms. Then
they are scaled to "fit" the actual game scores played so far.

Kenneth Massey, January 1999.

Massey Ratings |
Theory