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Subject: Re: how not to calculate performance

Author: Vincent Lejeune

Date: 15:47:26 10/23/04

Go up one level in this thread


On October 23, 2004 at 16:37:37, Stephen A. Boak wrote:

>On October 22, 2004 at 18:52:13, Uri Blass wrote:
>
>>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
>
>Dear Uri,
>What is the *correct* formula for a player who has won (or lost) all his games?
>:)
>Regards,
>--Steve


For such a player, the error margin = infinity

the perf = average opp +400 to +infinity



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