Author: martin fierz
Date: 21:12:53 03/17/04
Go up one level in this thread
On March 17, 2004 at 16:11:46, Dieter Buerssner wrote: >On March 17, 2004 at 15:08:55, Christophe Theron wrote: > >>Someone at the Israeli Chess Federation screwed up and I guess that now they are >>forced to keep this formula for reasons that have more to do with >>historical/political reasons than mathematical ones! :) > >I don't think so. Actually, their formula is slightly better in the range from >20% to 80% winning expectation on average, also the maximum error is smaller. > >>I think my formula is more accurate. And actually it's not _my_ formula. I have >>found it somewhere, but I do not remember where. > >Your formula is more accurate close to 50% winning percentage. > >>The real elo formula has the interesting property to be close to linear in the >>20%-80% winning percentage range, hence the 80% validity limit. > >Close to 20%/80% it is already signigicantly non linear, which favors a higher >multiplier to average this out a bit. The best multiplier for the 20-80 range >would be 7.55. > >But with pocket calculators, it is no problem to use the better forumla > >rating_differnce = -400 * log10(1/match_result-1) > >where match_result is the "winning-percentage"/100. That formula is correct, if >the elo system uses the "logistic distribution" and almost correct, if it uses >the normal distribution (only in the extreme tails, say < 5% or > 95% it will >make a difference). I am not sure, which it really uses. The German Chess >Ferderation seems to use the normal distribution, while USCF seems to use the >logistic distribution. In the FIDE handbook, I just find the tables. At the >tails of the given table, it does not fit either distribution totally >accurately. I found one article of Glickman once, which mentioned, that FIDE >switched to the logistic distribution, but actually numbers calculated from the >normal distribution fit the given table better ... > >Regards, >Dieter my impression was always that it was a normal distribution, and that the tables were slightly inaccurate because of rounding errors. i know the swiss federation uses the normal distribution. cheers martin
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.