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Subject: Re: Margin of error in ratings?

Author: Peter Fendrich

Date: 12:41:05 06/04/99

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On June 04, 1999 at 08:22:41, Arda Renkver wrote:
>Could someone refer to a source as to how to get these +61 -53 etc margin of
>error ratings points depending on the number of games played.Like in the new
>Swedish list; 182 games for CM6000 has higher margin than 900 games played with
>some other program.For example is just one game's margin of error in rating 800
>points? What is the maximum number of games required to be in the range of + and
>- 0.000...1 etc? What statistical formula or concept used other than ELO
>calculation as usual.

To estimate the standard deviation of the ratings there are
several options, giving about the same result, the SSDF method is:

       s=SQRT( (W(1-m)**2 + D(0.5-m)**2 + L(0-m)**2/(n-1) )
       A=1.96 * s/SQRT(n)

       where s is estimated standard deviation
             n     is the number of games
             m     is score/n
             W,D,L is the number of Wins, Draws and Losts respectivelly
             A     is the margin of error (for score, not rating points)
             1.96  is fetched from the Normal Distribution table to get
                   95% reliability
             SQRT  is the square root
             **    is the power of

    Now we have an 95% interval of scores from m-A to m+A

    Compute the ratings for m-A and m+A and here we go!

    This is done for each chess program.

//Peter Fendrich



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