Author: Uri Blass
Date: 23:12:51 10/23/04
Go up one level in this thread
On October 24, 2004 at 01:47:54, Stephen A. Boak wrote: >On October 23, 2004 at 18:47:26, Vincent Lejeune wrote: > >>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 > >Thanks, Vincent. I know the formula well. :) > >I was poking fun at Uri (just teasing) for complaining about 'logic' when in >fact the formula for all wins or all losses is purely arbitrary. > >[I've read that Uri is a mathematician, so I like to occasionally jump in and >comment when he seems to overlook something basic. All in good fun--I >appreciate his postings and chess programming contributions.] > >I asked Uri what formula would he suggest as 'correct'. I think that it is possible to calculate the performance of a player that get 1/2 point instead of 0 point and use the result as an upper bound for the performance of the player that got 0 points. It is not done. Another idea is to assume probability of win draw loss for every difference in rating and to calculate the maximal rating that the probability to get 0 points is 50% or more than it. This is going to be the performance of player who got 0 points. More generally I can define Performance of a player who got m point out of n points as the rating that the probability to get more than m points(or exactly m points if m=n) is equal to the probability to get less than m points(or exactly m points if m=0). Uri
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