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The CFC ratings system usually takes quite a shafting on this site, so I figure it's time for something positive about it.
I was looking through my results in 2010 recently and I came up with some surprising results. First I looked at my record against players whose ratings were lower than mine: 38-1-2
Well, that's great. It was, however, more wins than I'd thought I'd even had last year, so it was with dread that I looked through for my performance against players whose ratings had exceeded mine at the time of play. My dread was not met with disappointment: 0-13-2 was my record
Therefore, I have come tp the conclusion that I am living proof of a couple general statements:
1) The CFC does get people's ratings spot on at times.
2) Experts are indeed what masters eat for breakfast (and in my case, lunch, supper, and afternoon snacks).
So congratulations CFC! I am most definitely who you thought I was! Now it's just another ~1850 more people to go and we'll have the most accurate ratings system in the world!
It does work quite well for active players... I played 18 events in 2010 and in December I played a match against Alex Ferreira, who is also a very active player... amazingly, over a seven game match we both performed at exactly our own ratings (1970 and 2084).
However this did cause me notice something weird... considering our performance ratings matched our pre-match rating, one would expect our post-match ratings to be the same as the pre-match ratings... however I had gained 4 points and Alex lost 4.
It took me a while to account for this... it turns out that the performance rating posted on the website is always determined using the "unrated performance scale", and not the actual expected results scale....
Can anyone think of a reason why, for established players, the logarithmic scale (expected results scale) is not used to calculate performance? I suppose it must be because the log scale falters somewhat in the event of a perfect or zero score...
I had always thought that the linear approximation was used until last summer when the rating auditor told me last summer that the full non-linear function was used (not clear on when the transition was made or if his understanding was correct). I did not verify this one way or the other.
I know that some systems use a small adjustment in the case of perfect or zero scores to deal with the problem of infinities. (i.e. a score of 5 out of 5 is reset to something like 4.95 out of 5 for the purposes of calculating a performance rating).
I had always thought that the linear approximation was used until last summer when the rating auditor told me last summer that the full non-linear function was used (not clear on when the transition was made or if his understanding was correct). I did not verify this one way or the other.
I know that some systems use a small adjustment in the case of perfect or zero scores to deal with the problem of infinities. (i.e. a score of 5 out of 5 is reset to something like 4.95 out of 5 for the purposes of calculating a performance rating).
I think the linear approximation may be used on the on-line rating calculator. The performance rating column on the tournament crosstables is just for display purposes, and does not adjust for 350/400 point rating safeties, either.
I think the linear approximation may be used on the on-line rating calculator. The performance rating column on the tournament crosstables is just for display purposes, and does not adjust for 350/400 point rating safeties, either.
The performance rating matters for the calculation of provisional ratings (i.e. those with less than 25 games in the system). From the point of view of programming complexity, the calculation of a new provisional rating (i.e. someone with 15 games who plays an additional 5 games say) is trivial using the linear approximation (just requires the old provisional rating, and the new games). Using the nonlinear form requires looking up all the previous performances, parsing out the individual game results, pulling out all the opponents's ratings at the time, and then doing the caculation. The format of the data for the previous results means that this is all a bit awkward, although of course it can be (and is?) done.
The performance rating matters for the calculation of provisional ratings (i.e. those with less than 25 games in the system). From the point of view of programming complexity, the calculation of a new provisional rating (i.e. someone with 15 games who plays an additional 5 games say) is trivial using the linear approximation (just requires the old provisional rating, and the new games). Using the nonlinear form requires looking up all the previous performances, parsing out the individual game results, pulling out all the opponents's ratings at the time, and then doing the caculation. The format of the data for the previous results means that this is all a bit awkward, although of course it can be (and is?) done.
Yes, it is the value used for provisionals who have no rating protection.
Yes, it is the value used for provisionals who have no rating protection.
I'm not sure if Fred was trying to answer the question in parenthisis, but if so the formula on the site directly contradicts what he says...
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I have noticed that when performance is presented on chessbase crosstables (of top events) that they must be using the non-linear formula because when someone has an extreme score their perf. is often more or less then 400 points different from the average of their opposition... I remember that at one point they gave an explanation of how they represent perfect and zero score performances (I think they used .98 and .02 of expected score respectively).
I just thought is was highly strange when my performance (using the linear scale) equaled my pre-tournament rating, but my rating went up (because rating change uses a didfferent scale).
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