On Jan 14, 2009, at 2:15 PM, Rémi Coulom wrote:
Mark Boon wrote:
I'm not so knowledgeable about the ELO system and had a few
questions about how it's used by the CGOS server.
Firstly, on the CGOS server page there's an explanation of how it
works with a table of expected winning percentages vs. difference
in ELO ratings:
http://cgos.boardspace.net/ (towards the bottom)
This table is rather different from another table I found on the
GoBase page about the ELO rating system:
http://gobase.org/studying/articles/elo/
Is there a reason why they are so different?
CGOS probably uses the usual logistic formula:
http://en.wikipedia.org/wiki/Elo_rating_system#Mathematical_details
Arpad Elo, in his book, used the cumulative distribution of a
Gaussian instead. It has a similar shape, but it is different. FIDE
numbers are based on that older Gaussian formula.
Thanks for that link Remi. That same page states however that the FIDE
also switched to the method of using the logistic distribution. But it
doesn't say when that happened.
Mark
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