From: sloan@cis.uab.edu (Kenneth Sloan)
Subject: Re: FS level of chess
Organization: CIS, University of Alabama at Birmingham
Date: Wed, 7 Oct 1992 05:45:28 GMT

In article <1992Oct7.043024.17169@samba.oit.unc.edu> John.Risk@bbs.oit.unc.edu (John Risk) writes:
>I see many referances to F&S playing at the 2600 level, or their
>performance rating is 2650, or plus or minus something in this range.  Now
>I have played through some of these games and conceed that they are
>playing better that my Class A level, but my question is "how do we know
>at what level they are really playing"

The short answer is: we don't.

The long answer has two parts.  Part A is: evaluation by their peers, or
betters.  This is difficult when then number of "peers or betters" is
small, biased, and saddled with conflicts of interest.  Part B is: use
the customary ratings calculations and try to figure out how many
assumptions are neede to make the numbers fit.  Then, apply Occam's
Razor.

Analysis by players of demonstrated lesser strength is unreliable.
Of course, the closer the analyst is to a "peer or better", the more
reliable such a "rating by inspection" can be.

>
>...
>How do "I" know they are not both playing in the 2100 level.  

You ask:  "How many new assumptions, or twiddles, must I add in order
for this conclusion to fit the observations?"  In this case, you must
assume that *both* Fischer and Spassky have chosen this match to
deteriorate from their previously demonstrated strength.  Let's grant
for the moment that it would not surprise some people if 20 years had
eroded Fischer's strength.  But, you would still have to explain why
Spassky's strength had suddenly dropped by 400 rating points.

Of course, it's *possible* - it's just not the right way to bet.

>I suppose it is possible that both players are playing at the 3500 level,
>and no one recognizes it.

This, too, requires too many explanations.  

>...  It would seem that it will take subsequent
>matches, particularly in Fischer's case to validate ratings, but how can
>one ever validate playing performance in a match, except by concenses of
>their peers?

And, um, er,...how do you know who their "peers" are, if you don't make
some assumptions about their strength?  Suppose we could find 11 NM's
who are willing to testify that the games have been only at Expert
strength.  Why should we believe them?

The estimates can only be supported (or deprecated) by future (and
past!) performances in a much larger rating pool.  A central question
for any rating scheme is how consistent the various estimators are with
each other.  

Personally, I doubt that it is possible to estimate chess strength "by
concensus".  I'm not aware of even an attempt to construct and test such
a rating system.  If anyone knows of such a beast, I would be very
interested in hearing about it.  If anyone would like to try it - I'd be
happy to contribute a sampling of games played at a wide range of
official ratings.  I would be *very* impressed if anyone could take 10
games (say, at 100 point "current rating" intervals") and correctly rank
order them.  

-- 
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
Newsgroups: rec.games.chess