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Subject: Re: How many games are needed to find out which program is stronger?

Author: Bruce Moreland

Date: 00:16:50 09/03/99

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On September 02, 1999 at 20:02:55, Heiko Mikala wrote:

>And I say what you're saying is clearly wrong. Believe me, I learned this the
>hard way during the last ten years of work on my own chess program. I often had
>the case that in a first test match of about 30-40 games my program convincingly
>won a match, than let it play another, longer match overnight and during the
>next day, which it than lost. You always need the same amount of games, no
>matter how the score is after a first, short match. My experience after hundreds
>of test matches shows, that you need at least 70-80 games to be able to come to
>a conclusion. And you need some hundred games to be sure. Even if the first 15
>games end in an 15-0 score. Because the next 15 games may end 0-15. This is a
>frustrating fact, but it is *a fact*. It's frustrating, because for us as
>programmers it means, that we have to do much more time consuming testing than
>we would like to do.

It shouldn't work like this.  You can't take a selection from somewhere in the
middle of a long run of games, and use that to prove anything, but if you start
out and play some games, and one program wins a several games in a row, you
should be able to make a safe conclusion.

I would really like to understand the 15-0 and 0-15 situation.  That should
*not* happen.  That's not how math should work.  If you flip a coin 15 times and
it comes up heads each time, the odds of this happening completely by chance are
extremely small.  The odds that it would then come up tails 15 times in a row
are also extremely small, and combined they should be vanishingly small.

You can find a run where this happens, with two equal strength programs, but it
should have to be an extremely large run.

Maybe there is something going on that destroys the randomness of the whole
thing -- for instance it could be a problem involving a narrow book.

bruce



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