From: sloan@cis.uab.edu (Kenneth Sloan)
Newsgroups: rec.games.chess
Subject: Re: Looking for improvement suggestions
Date: 10 Apr 92 21:42:08 GMT
Organization: CIS, University of Alabama at Birmingham

In article <1992Apr10.181945.26728@cs.brown.edu> jhc@iris.UUCP (James H. Coombs) writes:
>..
>As an extreme example, Jorge Zamora went from 1900 to 2400 last year.
>He probably did not improve that much in one year but was seriously
>underrated to start with. 

I see no reason to believe that he was "seriously underrated to start
with".  You are assuming your conclusion.

> If a rating can be that far off at high
>levels,

Assumes facts not in evidence, no?

>...
> So
>when I face an opponent for the first time, I have to take the attitude
>that his/her rating is meaningless (i.e., I can't make it the basis for
>my plans, and I really shouldn't expect to win/lose).

Excellent conclusion - I'm only quarrelling with the reasoning.

>...
>Well, they are accurate scorings of tournament performance.  From them,
>we can estimate future performance, but this is a statistical
>estimation.  USCF gives 1 point for every 25 point difference in
>rating.  So, player 2000 can be expected to beat player 1800 three
>times out of four *over the long run.* 

Precisely.  There's no promise of anything more than that.

>I also wonder about relatively closed communities where the same people
>play each other over and over.  Couldn't you have Class D players in
>one area who are better than Class B players in another?  How does one
>make Master when there are no Masters to play against (haven't we heard
>this one about Louisiana?)?

Yes, indeed.  Players at the top, and the bottom, of a small rating pool
have exaggerated ratings.  This isn't usually a problem for the players
at the bottom, because (as you note) they are generally improving.  But,
ratings at the top can run away.  In practice, the players at the top of
the heap tend to take their rating points out of town, where they lose
them.  There are, however, periodic claims of significant differences
between ratings in different pockets of the country.  

>...
>Emphasis on "can be".  Consider Zamora.

I did, above.  But, sure - put the emphasis on "can be".  That weakens
the claim so much that I won't disagree with it.

>...
>Ah, but I think now you are changing the problem from one of predicting
>the result of the games that I am about to play to one of predicting
>the results of all players over the long run. 

Well, no.  That was the problem all along.  Everyone concedes that
individual performance can be affected by all sorts of things -
information about which is simply unavailable to the rating system.  No
one claims that the ratings are perfect.  If they were, there would be
no point in playing the games - no?


>
>I suppose that people who have played "a lot" of tournaments quit
>worrying about this sort of thing.

Somewhat.  Some players (especially teenagers, in my experience) tend to
get trapped in "ratings mania".  This way leads to sandbagging,
complaining about 3 point differences between privately calculated
ratings and published ratings, laying complicated game plans based on
the wall chart rating of your opponent, etc.  It's just an *estimate*!
It's a useful way to avoid mis-matches.  It helps you find a good game
in a different city.  It helps evaluate analysis freely offered (yes, it
acts a bit as a credential).  But it's not a perfect predictor.  There
are no observed anomolies which require the addition of epicycles to the
model to bring it into correspondence with reality.

There's no real reason to consider a ratings difference of 50 points to
mean very much at all.  In a young player, or a new player actively
studying, or an old player starting to fee the effects of age, the
published rating may be off by as much as 100 points, compared to the
true playing strangth.  As I noted in an earlier post - not playing for
6 months is likely to knock 100 points off your performance.

there is no way that the rating system can know these things.  There is
no way that these things can show up on the wall chart.  So - read those
numbers with a very fuzzy filter!  Don't castigate the system for not
being omniscient.

>
>On the other hand, the rating system does make it unlikely that I will
>be paired with someone who is twice as good as me. 


Not at all!  One of the uses that ratings are put to is to "seed" the
better players.  Go and pay your money to enter the Open section at the
World Open.  They'll be happy to find someone "twice as good as you" -
at least in the first round.

> Thanks for the discussion.  I concede!  

Oh dear!  Don't do that - it's just getting interesting.




-- 
Kenneth Sloan                   Computer and Information Sciences
sloan@cis.uab.edu               University of Alabama at Birmingham
(205) 934-2213                  115A Campbell Hall, UAB Station 
(205) 934-5473 FAX              Birmingham, AL 35294-1170