[computer-go] Go rating math information

[Andy]

Sorry, the KGS formula uses a constant k which is different from the
K-factor in Elo.
P(A wins) = 1 / ( 1 + exp(k*(RankB-RankA)) )

This would be equivalent to changing the constant 400 in:
P(A wins) = 1 / ( 1 + 10^((Ra-Rb)/400)) )

EGF has a similar scheme except of course they use different letters for
equivalent constants.  So this varying of k is what accounts for the fact
that upsets are more likely for weak kyu players than for dan players.

- Andy


On Jan 31, 2008 12:37 PM, Don Dailey <drdailey at cox.net> wrote:

> ELO ratings don't have to be absolute, just self consistent.   So if you
> beat someone 7.2% of the time,  that means you are about 440 ELO
> stronger than him.
>
> However, I don't understand what the K-factor has to do with anything.
> scaling it up or down doesn't change anything.  It's common practice to
> make the rating of strong players change more slowly as the result of a
> win or loss but that's not relevant here.
>
> The findings below indicate that differences between dan players is
> greater than the difference between kyu players.     So you could not
> assign a fixed ELO per rank but it would have to progressively get
> higher as the players get stronger.
>
> I don't know how David figures 1000 ELO,  but I would expect the
> difference to be much larger than that for 19x19 go.     I don't believe
> they are yet very close to 1 Dan.
>
> - Don
>
>
>
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