Author: James T. Walker
Date: 04:29:26 10/27/04
Go up one level in this thread
On October 26, 2004 at 03:08:09, Uri Blass wrote: >On October 25, 2004 at 18:21:23, James T. Walker wrote: > >>On October 24, 2004 at 17:02:44, Uri Blass wrote: >> >>>On October 24, 2004 at 13:04:07, Stephen A. Boak wrote: >>> >>>>On October 24, 2004 at 02:12:51, Uri Blass wrote: >>>> >>>>>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. >>>> >>>>Ok, Uri, I accept the challenge. >>>> >>>>Assume a player scores 0 points out of 10 total games. >>>> >>>>What Win, Draw, Loss probabilities should be used (arbitrary once again, for an >>>>unknown player's strength, who has scored m=0 out of m games--right?), and for >>>>what difference in rating? >>> >>>The opponents are players with known rating. >>> >>>We can calculate the probability of player with rating 1300 to get 0 points >>>against the players because we have some assumption about probabilities based >>>on the difference in rating. >>> >>>We can choose every different number than 1300 and calculate the probability for >>>every x so we have a function p(x) and later solve the equation p(x)=0.5. >>> >>>> >>>>What is the 'logic' for your choice of 'difference in rating'? That choice has >>>>to be illogical (totally arbitrary), when the new player doesn't yet have a >>>>rating, right? >>>> >>>>ELO does exactly that already--assumes the player is exactly 400 points less >>>>(i.e. assumes a particular rating difference) than his opponents' average >>>>rating, against which opponents he has scored m=0 points). >>>> >>>>What is a more logical rating estimate for the player than 400 points less than >>>>the average rating of his opponents? What is the improved 'logic' for your >>>>suggested rating approach? >>> >>>We want the best estimate for the rating of the player based on the results. >>>400 elo less than the average of the opponents is llogical because by that logic >>>if a player lose against 10 players with rating 1400 and 10 players with rating >>>2400 the player get 1900-400=1500 and it is clear that the player is weaker than >>>1500. >>> >>>Even in the relevant link minimal rating minus 400 and not average rating minus >>>400 was used but it is still illogical. >>> >>>> >>>>My thesis is that any suggested formula involves as much guessing, as much >>>>arbitrary choice, as much 'illogical' thinking (because it is totally arbitrary) >>>>... as the original +/- 400 points rule used in the ELO system. >>> >>>No >>> >>>You need to give an estimate for the rating. >>>It is logical to give smaller estimate to player that score 1/2 point and not to >>>player who scored 0 point. >>> >>>Every frmula that does not does not do it simply can be improved to a better >>>estimate easily. >>> >>>If the estimate for players that score 1/2 point is correct the estimate for >>>players who score 0 point need to be smaller(I do not know how much smaller but >>>it need to be smaller) >>> >>>If you lose against many players the estimate need to be smaller relative to the >>>case that you lost only against one of them. >>> >>>I do not know how much smaller but the formula should promise that it will be >>>smaller. >>> >>>It is possible to test different methods in practise by investigating real cases >>>of players who got 0 points and find their real level based on games against >>>weaker opponent. >>> >>>The problem what is the best estimate is a practical problem and I did not >>>investigate it(incestigation can try many possible methods and testing their >>>errors in predicting future results when you choose the method that reduce the >>>error to be minimal) but one clear rule is to give better performance for >>>players who do better results. >>> >>>It was not done by the link that I gave. >>> >>>Uri >> >>Uri it is impossible to come up with a practical score for anyone who is winless >>or undefeated in his/her first few games. It does not matter who they play or >>what the opponents rating is. The performance formula is used only to establish >>a "performance" rating in a short match/tournament. If its the first rated >>games you have ever played then you are only given a "provisional" rating untill >>a more accurate rating can be established in later tournaments/matches. Someone >>rated 400 points above you has about a 91% chance of beating you and you have >>only a 9% chance of winning. If you think you can give an accurate rating to >>someone who has never won a game in his life and has only played 4 games then >>you are dreaming. > >I did not claim that you can give an accurate rating. >rating is not accurate. >I only claimed that you can give a better estimate. > >rating is always an estimate and even if you know only the results you can use >them to calculate some estimate. > > > Computer programs calculate the performance rating and nobody >>actually looks at the games to see how strong/weak the player may actually be >>(In their estimate). In fact by the time they play their next 4 games they may >>have improved by 400 points. I know several people who have done this because >>they waited 2 years before playing again. > > >It only suggest that the dates of playing should be also used to calculate >performance and old games should get smaller weight. > > In the case of the one win scenario >>you mention the link you gave gives two "ratings". The one you quote is a >>"performance" rating and the second is the actual "new" rating. In the problem >>you quote there is no reason for these two ratings to differ. They should both >>show 1067. Therefore the link has improperly applied the formula which >>calculated the score below 1000. IMHO. >>Jim > > >The estimate for 0 out of 12 against 1400 players should be smaller than the >estimate for 0.5 out of 12 against 1400 players. > >The estimate for 0 out of 12 against 1400 players should be smaller than the >estimate for 0 out of 4 against 1400 players. > >If these rules are not kept then my opinion is that the estimate can be >improved. > >Uri I still don't follow your logic. Your assumption that 0/12 is worse than 0/4 is not logical. In both cases the actual rating of the person playing may be something like 500. In fact it could be the same person that played 4 games one day and then a week later played another 8 games. As you say it is only an estimate untill enough data can be obtained to make a more accurate assesment. Jim
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.