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Subject: Re: Junior - Crafty NPS Challenge - a user experiment

Author: Sune Fischer

Date: 15:38:06 11/24/03

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On November 24, 2003 at 12:59:39, Rémi Coulom wrote:

>>I don't think that doesn't necessarily contradicts what you say though.
>
>No, it does not.

Sorry I managed to fumble up that sentence, I think we agree though that the
boolean question of whether p0>p1 does not depend on the number of draws.

>>>If I cannot convince you, perhaps have a look at Rémi Coulom's paper, available
>>>from http://remi.coulom.free.fr/ (inside
>>>http://remi.coulom.free.fr/WhoIsBest.zip). One cite from that paper:
>>>
>>>"This proves that the likelihood that the first player is best does not depend
>>>on the number of draws."
>>
>>Something to read tonight perhaps :)
>
>The paper is a bit mathematical, but the fact that the likelihood does not
>depend on the number of draws can be explained intuitively rather easily:
>imagine a game called "chess+" where no draw is possible: each time a game is
>drawn, the two players start over from the initial position until one player
>wins. Draws are not counted. For the exact same sequence of games, depending on
>whether you consider they play chess or chess+, the score will be 1006-1000 or
>6-0. Obviously, the likelihood that one is better than the other is the same.
>
>Of course, this is true only if the hypotheses are true: games are independent
>random events, and the prior is uniform (which is reasonable in comp-comp
>matches without learning).

While reading it I managed to convince myself you are right.

Intuitively it seems obvious that if the normalization constraint
p0+p0.5+p1=1 is the only correlation between p0 and p1, then
p0.5 isn't going to have any say in whether p0>p1 or not, right?

The only exception is if p0.5=1, but then we wouldn't have a three parameter
distribution in the first place which is sort of the assumption.

-S.

>I hope this message will save some mathematical reading for some.

>Rémi



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