From: sloan@cis.uab.edu (Kenneth Sloan)
Subject: Re: Inflation in ELO's system
Organization: CIS, University of Alabama at Birmingham
Date: Fri, 9 Oct 1992 17:02:39 GMT

In article <4065@cvbnetPrime.COM> fdeming@cvbnet@prime.com (Frank Deming {x6088}) writes:
>Given that at the lower rating levels there is a high degree of joining the
>rating system and then leaving it, do these individuals give an upward push to
>the rating system.

No.

>1. For the sake of argument, let say that 3 out 4 players that join the
>   rating system are in it only for the short term. The short term meaning
>   in this case they only ever establish provisional ratings. They are
>   typically 
>   weak, but not always.

OK.

>2. In receiving a provisional rating, they gain this rating number, but also
>   at the same time they contribute to the rating loss or gain of their
>   opponents. 

Remember that these provisional ratings are not "real" - in the sense
that no actual rating points are created.  The rating points themselves
only enter the system when the rating is *established*.

>   For the new provisional player, their rating adjustments are not on a net
>   basis, as I understand, but their opponents are.

Correct.  In a new player's *very first* tournament, his provisional
rating is calculated first.  And then...his games are rated as if his
pre-event rating were his newly calculated provisional rating.
So...there is no net effect on his opponent's ratings (effectively,
these players exchange rating points among themselves, through the new,
unrated player.

In subsequent tournaments, the new player has a provisional rating.  His
rating is still calculated by the Performance Rating calculation, and no
rating points are created until he receives his established rating.  His
opponents' ratings are calculated as if his provisional rating were an
established rating.

Notice: *most* players improve their tournament performances during the
provisional rating period.  They have to get used to playing in
tournaments, handling the clock, etc.  So, if anything, these new
players contribute to ratings DEflation during their provisionally rated
lifetime. Their opponents, as a group, lose rating points - which
disappear from the system.  If the same games had been played while the
provisionally rated player had an *established* rating, then he would
win those rating points -- and the points would stay in the system
(until he retired, taking them with him).  Instead, these points
disappear immediately.  Meanwhile, the provisional rating rises more
rapidly.  Thus - the provisional rating system *minimizes* the effect of
a new player's rapid early improvement, but it does not *eliminate* the
effect, which is still DEflationary.

For these reasons, Elo recommends (under 3.7 Deflation Control
Processes, subsection 3.72) 

    "...compute the provisional ratings after
    the new players have been rated [this was covered in 3.71 - as
    above], and use the post-event provisional ratings when calculating
    the ratings for the other players.  This maximuzes the data base for
    the new ratings, and the isolationary effect lessens as the
    confidence level increases.

    The novices, the juniors, or any other group may similarly be rated 
    early in the sequence, and their post-event ratings used when rating
    the remaining players, with similar effect.  This process is often
    advisable when juniors are competing with established adult players.

I'm not certain how New Windsor handles this right now - I believe that
they rate UNRATED players first, but don't know if they rate
PROVISIONALs early also.  I do not believe that they handle juniors
separately.  

Elo spends 1.5 pages on this - detailing:

    3.71 Appropriate treatment of unrated players.
    3.72 Modified processing of provisionally rated players.
    3.73 Adjustment of K
    3.74 Corrective additions for exceptional performances
    3.75 Feedback processes
    3.76 Treatment of new players

USCF uses (has used) most of 3.71-3.75.  FIDE uses (according to Elo) a
variant of 3.76.  

>3. Given that they are weak players, in typical tournaments, what are their 
>   effect on the net ratings of their opponents. In many open
>   tournaments, these 
>   new weak players, do get trounced badly, and leave the game. Do they in the
>   games they play, contribute net points to their opponents. Since
>   these players  
>   enter and leave with provisional ratings, it would seem that their main 
>   contribution would be their net(+/-) effect on the other players. An
>   example 
>   of this could be:
>      before an individual is in the pool, the pool has x points in it(not 
>      an average)
>      after the individual leaves the pool, he has contibute y(+/-) net points
>      to the pool.
>      Look at this before and after, it is clear what the provisional
>      player was 
>      rated while in the pool does not matter.

See above.  There is a second order effect.  The very first tournament
has no (or minimal) effect on opponents' ratings (taken as a whole).
Subsequent tournaments are likely to *subtract* ratings from the pool
(because the new player is likely to perform better in his second
tournament than he did in his first tournament).  Conversely, if a
player does fantastically well in his first tournament, and then bombs
out - he will have added a few rating points to the pool, without ever
having actually entered the pool.  Again - the question is: which
scenario takes place more often?  The absolute provisional rating does
not matter - it is the time-course of the provisional rating which
counts.  If a player's provisionall rating INcreases monotonically, then
he removes rating points from his opponents (and from the rating pool as
a whole); if the provisional rating DEcreases monotonically, then rating
points are added to the rating pool.

>
>
>Next Question on Inflation, given that the K factor is 32 for under(2100?),
>24 for under 2400(?) and 16 for above, is this not a recent concession
>to rating 
>inflation?

No.  Our reading today is from Chapter 1, verse 63:

    "The *coefficient* K reflects the relative weights selected for the 
    pre-event rating and the event performance rating.  A high K gives
    high weight to the most recent performance.  A low K gives more
    weight to the earlier performances.  Thus K may be used as a sort of
    player development coefficient to recognize the varying rates at
    which change occurs in a player's performance.  In actual practice,
    K may range between 10 an 32.  The lower value 10 is used in FIDE,
    where rated events are longer and player proficiencies are more
    stable.  USCF uses the higher value 32, since over 80% of the
    tournaments rated are weekend events of six rounds or less, and
    player proficiencies vary widely." 

When a game occurs between two players with the same K (and both players
have established ratings), the rating system is a zero-sum proposition.
What one player wins, the other player loses.  When a game occurs
between two players with different K, the player with the higher K sees
his rating change (either up, or down) faster.  Players at the top end
of the scale are assumed to have very stable chess strength (on the
grounds that most of the time people improve, and when you are at the
top there is no longer much room for improvement) - so a lower K is
appropriate.  These players also play more games (in general) over a
given period of time.  Young (and in general, weak) players have lots of
room for improvement, and often improve dramatically over a very short
period of time.  Using a large K for these players would allow their
ratings to track their strength more accurately, without "penalizing"
the players who used to be their superiors, but who are now their peers
(or worse).

USCF used to deal with this problem with a USCF 1000 rating floor.  As I
recall (please correct if you work in New Windsor and know for sure),
once your published, established rating was over 1000, it was not
allowed to fall below 1000.  This no longer appears to be the case (I
know of an individual who has had published ratings above and then below
1000) - the more general "rating floor every 100 points" is in place,
instead. 

>
>Last Question: What is the name and publisher of Elo's book?

The Rating of Chessplayers, Past and Present, second edition, by Arpad
Elo, Arco Publishing, Inc.

ISBN 0-668-04721-6

Published under grant from the American Chess Foundation, New York 
Copyright 1978 by Arpad E. Elo.  First published 1978. Second Edition
1986.
Artwork ad filmset by Zastrow Studios, Thiensville, Wisconsin, U.S.A.
Second Edition printed in the Philippines by Vera-Reyes, Inc.

It's listed in the Chess Digest catalog as B-115.  List $10.95 ours
$9.95.

I got my second edition from them in July, and paid $9.95.  Someone has
recently reported to me that they tried to order it and was told that
the price was $25+.  I haven't confirmed that report.

My second edition is a fairly sturdy paperback.  My first edition is
hard cover.  Perhaps the $25+ second edition is a hard cover version.
There is very little difference between the first and second editions,
so if you can find a used first edition it will probably tell you
everything you want to know.

Chess Digest: 1-800-462-3548 (Visa & MC)
        FAX:  1-214-869-9305 (Visa & MC orders only)
Customer hours 10am. - 5pm.(CST)

Have I left anything out?

Enjoy!




-- 
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
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