From: sloan@cis.uab.edu (Kenneth Sloan)
Newsgroups: rec.games.chess
Subject: Re: Inflation in ELO's system
Date: 8 Oct 92 15:28:34 GMT
Article-I.D.: cis.1992Oct8.152834.27607
Organization: CIS, University of Alabama at Birmingham

In article <1992Oct8.101844.17058@ai.univie.ac.at> juffi@ai.univie.ac.at (Johannes Fuernkranz) writes:
>... I always thought that the problem is that the average rating is INcreasing
>and not DEcreasing (I may be wrong on that).

I haven't seen any evidence presented which demonstrates this, but let's
assume that it is true.  In the USCF system (for example) various
twiddles have been introduced (bonus points, feedback, rating floors,
etc.) which distort the pure Elo system.  Some of these have had the
explicit purpose of combatting DEflation; other have had other
justifications.  The point is - any such mechanism needs to be carefully
balanced against the natural DEflation pressures.  If they overcorrect,
then you get INflation.  [bogus analogy alert!] You car will natrually
slow down, unless you balance frictional losses by pushing on the
accellerator.  If you car happens to be speeding up, this does not
constitute an argument that "all cars naturally speed up".

>... I'd also like to know why the 
>USCF ratings are about 150 points higher than European ratings.

First, they measure different rating pools (both different sets of
players, and different kinds of events).  That ought to be reason
enough.

Second, players who are rated in both systems tend to be at the top of
the USCF pool, and the bottom of the FIDE pool.  There are "tail
effects" which make virtually all rating schemes just a bit squirrelly
at either end of the rating pool.  Usually, no one cares about this,
because the number of people involved is so small, compared to the
rating pool as a whole.

Finally, I don't believe that there are any principled attempts to "fix"
this "problem".  As with {IN | DE}flation, this could be done by
constant monitoring and gradual tweaking of the parameters of one, or
both, rating pools.  The question is: is it worth it?  

For example...USCF might declare that FIDE-rated players in the USCF
pool would have their USCF ratings adjusted adaptively towards their
FIDE rating.  This would cause these players' USCF ratings to track (on
average) their FIDE ratings.  The interactions between these players and
the rest of the USCF pool would, in turn, push and pull on the upper
tail of the USCF rating pool.  The effect on USDF 1200 players would
be....minimal.

So - if the goal is to make the rating scales match, it could be done.  

The deeper question is: if ratings are an estimate of chess strength,
why is there a large difference in the estimates produced by FIDE play
and by USCF play.  The answers are:
 0) is there really a big difference?
 1) if there is, then perhaps the answer is that FIDE chess is
    somehow different than USCF chess.  Even now, USCF is establishing
    separate ratings for "regular" and "Quick" chess.  We might well ask,
    "Why aren't the ratings the same?"  Or, "What correction factor do I
    use to convert a regular rating into a QuickChess rating".  
    The answers are: "because the games are different", and "there isn't
    one".  [Well - there isn't one which can be justified on theoretical
    grounds - it may well be that we can study the two ratings
    distributions and derive an empirical transformation.  But then
    we would still be left with the question of "why".



-- 
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