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Home > Archive > Chess politics > April 2005 > Ratings experts: Please explain
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Ratings experts: Please explain
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| Angelo De Pa1ma 2005-04-07, 6:07 pm |
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I was recently browsing the MSA and noticed that one of my buddies in
Hackettstown had recently gained 52 rating points in a quad (not run at the
H'town club). This fellow had a performance rating (PR) of 2194 over 3 games
(2.5/3), which is pretty decent for a 1789 player but jeez, it's only 3
games. His PR was 405 points above his pre-tournament rating.
I then visited my own MSA page and looked up my result from the USATE. My PR
over five played games (4.5/5) was s a healthy 2303 but I "only" gained 41
points, from 1853 to 1894. My PR was about 450 points higher than my
pre-tournament rating.
I thought the discrepancy -- +450 over five games with a 41 point gain, vs.
+405 over 3 games and a 49 point gain -- was odd so I did a little
experiment.
I plugged 2303 (my PR from the USATE) into five of the opponent rating boxes
in the rating calculator, 1853 (my pre-USATE rating) into the "current
rating" box, and 2.5/5 as my score. Of course I get the same 2303 PR but
instead of 1894 my "new rating" is 1920, a nearly 30-point increase over the
same 2303 performance achieved with a range of opponent ratings.
Can anyone explain why and how this can happen? I always thought equal PRs
were, well, equal. Are some PRs more equal than others?
Please don't say the calculator is only approximate because it's predicted
our club members' ratings to within 1-2 points every time I've used it.
Besides, the calculator quirks don't explain my basic scenario since these
are actual, USCF-calculated ratings.
Angelo
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| David Kane 2005-04-07, 6:07 pm |
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"Angelo De Pa1ma" <adpspammersgotohell@tellurian.net> wrote in message
news:ouadnUH0xptyA83fRVn-1w@garden.net...
quote:
> I plugged 2303 (my PR from the USATE) into five of the opponent
rating boxes
quote:
> in the rating calculator, 1853 (my pre-USATE rating) into the
"current
quote:
> rating" box, and 2.5/5 as my score. Of course I get the same 2303 PR
but
quote:
> instead of 1894 my "new rating" is 1920, a nearly 30-point increase
over the
quote:
> same 2303 performance achieved with a range of opponent ratings.
>
> Can anyone explain why and how this can happen? I always thought
equal PRs
quote:
> were, well, equal. Are some PRs more equal than others?
>
One possible explanation is that some
PRs are more significant than others.
Consider 2 identical 2300 performance ratings:
W1800, W1800, D2300, L2800, L2800
vs.
2.5 points vs. 5 2300's
The 2nd will affect someone's rating more
because all of the games are significant.
If the opponents you beat are far away from
your performance rating, their significance
is less, and they don't affect your rating as
much.
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| Angelo De Pa1ma 2005-04-07, 6:07 pm |
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I was under the impression that (2.5 x 2300 x 5) = 2.5 x (2300 + 1800 + 1800
+ 2800 +2800). I've examined the formula and don't see anything (obvious to
me) that suggests otherwise.
Angelo
"David Kane" <davidekane@comcast.net> wrote in message
news:cLqdnbw4xecCLM3fRVn-vA@comcast.com...
quote:
>
> "Angelo De Pa1ma" <adpspammersgotohell@tellurian.net> wrote in message
> news:ouadnUH0xptyA83fRVn-1w@garden.net...
>
> rating boxes
> "current
> but
> over the
> equal PRs
> One possible explanation is that some
> PRs are more significant than others.
>
> Consider 2 identical 2300 performance ratings:
> W1800, W1800, D2300, L2800, L2800
> vs.
> 2.5 points vs. 5 2300's
>
> The 2nd will affect someone's rating more
> because all of the games are significant.
> If the opponents you beat are far away from
> your performance rating, their significance
> is less, and they don't affect your rating as
> much.
>
>
>
>
>
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| David Kane 2005-04-07, 6:08 pm |
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"Angelo De Pa1ma" <adpspammersgotohell@tellurian.net> wrote in message
news:AvadnX8mBeu0Js3fRVn-gw@garden.net...
quote:
>
> I was under the impression that (2.5 x 2300 x 5) = 2.5 x (2300 +
1800 + 1800
quote:
> + 2800 +2800). I've examined the formula and don't see anything
(obvious to
quote:
> me) that suggests otherwise.
>
> Angelo
Well you haven't stated exactly what math
you think should be relevant, but the average opponent
rating isn't even relevant for determining performance
rating in the general case. That is an approximation useful
when the opponents have ratings in the linear portion
of the winning expectancy curve. The performance
rating is the rating that predicts the achieved result,
taking into the actual non-linear winning expectancy
formula.
Your original assumption that identical performance
ratings should have the same effect on rating
(independent of the rating mix of the opponents) is
unfounded for the reason I gave. What matters
is the expected vs. actual, so some results don't
matter
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