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Aduke.1929 net.chess utcsrgv!utzoo!decvax!duke!bcw Sun Mar 28 14:16:13 1982 Re: Elo rating system

It's quite true that there are strange things which can happen with the provisional rating formula. The problem is that before someone has built up a sufficient history, there isn't much that can be done with improving the accuracy of provisional ratings.

The provisional rating hasn't been the only problem; recently the USCF changed from an approximation of what was believed to be the "true" winning probabilities to the exact formula (it is believed, based on empirical and some theoretical considerations, that the probability of winning can be expressed as an S-curve centered about the difference in ratings). The approximation used flat lines at the asymptotes and a linear approximation in between (making it a sort of Z-curve). This lead to peculiarities in the range of 250-350 rating points difference between the players and the USCF changed it to the true S curve about two years ago.

There's a fairly extensive literature on rating systems but as far as I know the Elo system is considered to be the best that anybody has been able to come up with to date.

Bruce C. Wright @ Duke University

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