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Subject: Re: ELO Calculations

Author: Kolss

Date: 04:48:56 04/16/05

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On April 15, 2005 at 17:58:30, Anson T J wrote:

>Does anyone know the accurate formula to work out ELO performance based on an
>estimated elo for a player and the % success?
>
>For example if Hydra played against Kasparov (2812) and scored 45%, what how
>would we work out Hydra's elo performance in this match?
>
>I remember somebody posted a very accurate formula using logs, if they could
>point me to the post or write the formula again in here I would greatly
>appreciate it.
>
>Many thanks.

Hi,

Def.:
diff = ELO Difference;
p = fraction of points scored (0 < p < 1).
lg = log base 10

Formulas:

diff = 400 * lg(p / (1 - p))

p = 10 ^ (diff / 400) / (1 + 10 ^ (diff / 400))


Example:

With a score of 45 %, we have p = 0.45, this gives us diff = -35, therefore with
an opponent ELO of 2812 a performance of 2812 - 35 = 2777.

In the other direction, if your ELO is 2777 and your opponent's is 2812, diff =
-35, which gives us p = 0.45, which is your expected score in a match.

Hope this helps!

Best regards - Munjong.



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