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Subject: Re: Standard deviations -- how many games?

Author: Rolf Tueschen

Date: 17:00:30 01/23/04

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On January 23, 2004 at 18:33:52, Dann Corbit wrote:

>On January 23, 2004 at 18:20:34, Russell Reagan wrote:
>
>>On January 23, 2004 at 15:24:31, Dann Corbit wrote:
>>
>>>30 experiments is a fairly standard rule as to when you should start to trust
>>>the results for experimental data.
>>
>>So what does this mean for chess engine matches? You need at least 30 games? Or
>>30 matches? If matches, how do you determine how long each match should be?
>
>It means less than 30 games and you cannot trust the answer.
>With more than 30 games, confidence rises.
>
>I bring up the number 30 because it is important in this case.  If you run (for
>instance) a 15 game contest, it would be dangerous to try to draw conclusions
>from it.  With 30 games or more, even something that does not perfectly model a
>normal distribution will start to conform to the right answers (e.g. the mean
>calculation will be about right.  The standard deviations will be about right
>unless sharply skewed).
>
>30 games is the break even limit where deficiencies in the choice of a normal
>distribution as a model start to become smoothed over.


About what measurements you are talking here? Of course the N is right for
normally distributed variables but what do you "measure" with chess games?
Second question: when you have almost equally strong chess programs you are
implying that after 30 games you can make a sound conclusion which one is
stronger? - If you think you can answer with YES, then I doubt it. Of course, if
you then do - what the SSDF is doing - matches between two unequal progs you can
well get clear results after 5 games. But of course 30 games will be a good
profit for the better program. Also if tests have been known where a directly
concurring prog usually gets less points against this out-dated prog...

What I want to say is this. It was often explained here in CCC. For good results
you must enter into some thousand games mode. 30 games is just for laughter. It
is an irrelevant species.

Rolf



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