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Subject: Re: how not to calculate performance

Author: Uri Blass

Date: 15:52:13 10/22/04

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On October 22, 2004 at 18:30:34, James T. Walker wrote:

>On October 22, 2004 at 13:32:57, Uri Blass wrote:
>
>>go to the following link
>>
>>http://georgejohn.bcentralhost.com/TCA/perfrate.html
>>
>>enter 1400 for 12 opponents
>>enter 0 for your total score
>>
>>Your performance is 1000 but if you enter 1 to your total score your performance
>>is only 983.
>>
>>It seems that the program in that link assume that when the result is 100% or 0%
>>your performance is 400 elo less that your weakest opponent but when your score
>>is not 100% it has not that limit so they get illogical results.
>>
>>Uri
>
>My take on this is they are using a bad formula or have screwed up the program
>to calculate the Rp.
>The USCF uses Rp=Rc + 400(W-L)/N

It seems that the USCF does not do it in that way

They admit that the formula is not correct for players who won all their games

Note:  In the case of a perfect or zero score the performance rating is
estimated as either 400 points higher or lower, respectively, than the rating of
highest or lowest rated opponent.

It is probably better to estimate the preformance based on comparison to  the
case that the player did almost perfect score.

Uri



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