From: sloan@cis.uab.edu (Kenneth Sloan)
Subject: Re: Inflation in ELO's system
Organization: CIS, University of Alabama at Birmingham
Date: Mon, 28 Sep 1992 18:16:43 GMT

In article <1992Sep28.171802.1@ulys.unil.ch> jboschun@ulys.unil.ch writes:
>In the various questions about Fischer's strength somebody talked about
>inflations in ELO ratings...
>Is somebody able to give a quantitativ evaluation of it from 1972 and so
>to give, for instance, the value that Kasparov would have had at that time
>(or the value of the Fischer of '72 now) ?

No.

>More can somebody explain the exact origin of the ELO's inflation (is it
>coming, like in the case of money, from the increasing number of chess
>players or is there other reasons to that fact, I once heard about a bad
>management of the system ?) ?

Neither.  There is an *de*-flationary pressure - which can be managed.
Alas, this management is often controversial - it also can tempt the
managers into all sorts of odd twists and turns.  Sometimes, the
deflation is "overmanaged" and people perceive an overcorrection - i.e.,
inflation.

The deflationary pressure comes from the (observed) fact that most
players leave the rating pool with a higher rating than they had when
they entered the pool.  When rating points are managed as a conserved
quantity, these retiring players slowly but surely will remove all of
the rating points from the pool.  The remaining players compete for
fewer and fewer rating points, and the average rating must (of course?)
go down.

This is more of a problem, I suspect, for national rating pools such as
the USCF pool, where a "typical" player may be given an initial
established rating in the 1000-1200 range, and the player stops playing
when his rating is in the 1500-2000 range.  The initial established
rating effectively mints brand new rating points.  The player's
retirement takes these rating points, plus the ones taken from his
opponents in mortal combat, and buries them.  Thus, every player removes
some number (let's say approximately 500) of rating points.

In the FIDE pool, my guess is that new players enter at about 2400 and
leave at about 2500, on average.  Only in rare cases do they leave at
their absolute peak - most players give back a few rating points in
their old age.  There may also be more "flash-in-the-pan" players who
establish a relatively high initial rating, and then retire after being
beaten into submission - donating a few points to the pool.  So...FIDE
deflation may be less of a problem than USCF deflation.

What to do?  Everyone is unhappy when it becomes increasingly difficult
to garner rating points.  Players especially feel that their strength
has gone up, but their rating has stayed the same (or fallen!).  The
solution is to print more money (oops, I mean rating points)!  Some
mechanism must be used to insert rating points into the system to
balance out the ones disappearing with retiring players.

The USCF have experimented with several schemes.  Now that they have the
"rating program of the week" system, they will surely experiment with
more clever ideas.  These mechanisms are all (of course?) inflationary.
Sometimes they are too inflationary, sometimes not.  In either case,
some people, on hearing of these schemes, but not understanding the
reasons behind them, leap forward with the charge "Inflation! Ratings
just aren't worth what they were when I was a youth and had to walk
three miles through 6 feet of snow to ..."

I'm not familiar with FIDE deflation-control mechanisms.  I would be
very interested in hearing the details, from someone who actually knows.

-- 
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