Sean Hewitt wrote:I'm not overly concerned about the finite numbers (whether a player is 100, 150 or 1276!) as long as he scores 75% against a player who is graded 25 points below him.
Sean, it has been pointed out many times on this forum that this 75% "predicted score" is being abused. For example by myself and exhaustively and convincingly by Brian Valentine.
I will quote myself for the sake of convenience:
Paul McKeown, Re: New grades (split from Editorial thread), Wed Sep 03, 2008 2:55 pm wrote:A chess rating is an ESTIMATE of a statistical parameter not the actual value. So it can never be known for certain that a player is 1700 Elo player. Sometimes he plays as a 1600 player sometimes as an 1800 player. Assume that a given player is 100% certain a 1900 player (an impossibility of course) who plays a player with a 1700 rating. Elo tables predict a 76% result for the stronger player. But what if the weaker player plays 50% of the time as a 1600 player and 50% of the time as an 1800 player? Then the stronger player will achieve 50% of his anticipated score against a 1600 and 50% of his anticipated score against an 1800, which is 0.5 x (0.64 + 0.85) = 74.5%. In otherwise, because of the uncertainty in the playing strength of the weaker player, the stronger player will not achieve his "theoretical" Elo score.
At the time I wrote that there were some burblings from the shires about, "but we use the Clarke system", which I found very dull, as the principle is the same.
I could of course have quoted some more recent and much more theoretically grounded analysis by Brian Valentine to the same effect. Or alternatively I could have quoted A Comprehensive Guide to Chess Ratings, by Professor Mark E. Glickman, one of the reference works on this subject.
All with the same conclusion, the "75%" is not a prediction, but an upper limit to the predicted score of the higher ranked player.
What is being done to the grading system is vandalism, pur sang, supported by dubious analysis, opposed by most of the chess public who have had grades for long periods and see no obvious reason to assume that grades are not reasonably correct, and rammed down their throats by an acolytic clique of believers.
The grading system will not be improved one jot by this exercise and no doubt a change to an Elo based system will follow within a few years as a corrective consequence of this damaging upheaval.