From: sloan@cis.uab.edu (Kenneth Sloan)
Subject: Re: Inflation in ELO's system
Organization: CIS, University of Alabama at Birmingham
Date: Tue, 29 Sep 1992 21:25:44 GMT

In article <1992Sep29.202709.26356@noose.ecn.purdue.edu> watsonb@alcohol.ecn.purdue.edu (Bradley S Watson) writes:
[brilliantly, correctly answering several ... factually challenged ...
 notions about the ELO system]

except...

>Bonus and feed-back points were intended to counter the massive deflation that
>occured in the 70's because of the Fischer boom.

Strictly speaking, I believe that both bonus and feed-back points were
*intended* to make the system a bit more accurate in the short term, and
only indirectly acted to control long term deflation,.  The inaccuracies
(due to lower rated players improving faster than the system could track
them) did tend to produce deflation, but I think that the motivations
were primarily couched in terms of accuracy and fairness, rather than
systematic deflation.  Bonus points were intended to boost young and
improving ratings (a larger K might have been more consistent - but I
don't recall much discussion of the manipulation of K in those days).
Feed-back points were intended to compensate the unlucky opponents of
these whiz-kids.

>..  During 1980 they carried
>it even further by simply giving points to all active players under 2100 each
>supplement.

This was a frank anti-deflation mechanism.  It is the most honest,
straightforward method of tweaking the distribution to conform to a
priori expectations, and has few side-effects other than the intended
anti-deflation.   But, many people recoiled from the seemingly arbitrary
nature of simply "giving away" rating points (especially those rated
above 2100, who felt that that had 'earned' their rating points [usually
by walking through 6 feet of snow] and were outraged to see their
inferiors' ratings boosted without hard work).  Feedback and bonus
points had the merit of being tied to exceptional performances - so only
the "right" players had their ratings adjusted.

If I had my druthers, I think that I would favor a "per-game tax" - a
number of rating points added (or subtracted) for each game actually
played.  The "tax" could be modified each year based on a statistical
analysis of the rating pool, and could perhaps be a function of the
player's rating.  The idea is similar to a "budget plan" or an "escrow
account".  Notice that while the points would initially be awarded to
the players, the results of future games would continue to redistribute
these points throughout the chess economy.  [NOTE: this scheme could
also be applied *without detection* - since the amount of the "tax" is
surely down in the noise compared to the other uncertainties in ratings
calculations.]

The amount and distribution of the "tax" depends on complex issues
pertaining to the "correct" distribution of ratings.  Proper
administration would require the moral equivalent of a Federal Reserve
Board.  Once, long ago, it was possible to assemble a small, dedicated,
competent, and dis-interested committee capable of performing this task.
Now, alas, I doubt that it could be done.  More's the pity.

>
>While we're on the subject of ratings, does anybody out there
>know why FIDE ratings are always multiples of 5?

Fiat, I believe.  Personally, I don't see much point in *published*
ratings more precise than 25 points.  On the one hand, in a world where
professional careers can be affected by placing on the ratings lists
(invitations, etc.) it is better to have a group tied at, say 2555,
instead of 5 ratings at 2553,2554,2555,2556,2557.  On the other hand -
the poor schmuck rated 2552 (2550) is now separated by 5 points from his
rival at 2253 (2255) - rather than being in the same group.  It raises
the quantization noise, but eliminates many false differences.

Actually, it's no more arbitrary than the convention that USCF ratings
are always integers.  You wouldn't want a rating of 1846.32415926, would
you?  Unless, of course, it gave you a tiebreak over your lifelong
rival, with a rating of 1846.32415925...  And, you might prefer a rating
of 2199.999 to 2200 (well, I'd prefer the 2200 - I understand that there
are some unsavory types who would actually prefer the 2199.999).









-- 
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