From: sloan@cis.uab.edu (Kenneth Sloan)
Subject: Re: The ICS rating system (was Re: Why I Hate the ICS rating system.)
Organization: CIS, University of Alabama at Birmingham
Date: Mon, 9 Nov 1992 19:23:51 GMT

In article <JARMO.92Nov9131220@korppi.cs.tut.fi> jarmo@cs.tut.fi (Sorvari Jarmo) writes:
>...
>How about if the opponents of novices would not be affected at all?
>So that after 20 games, new players would enter the pool with a more
>realistic approximation (based on the +/- 400 rule) of their strength
>...

Under slightly idealistic assumptions, this is what happens under the
USCF system - to the extablished players *as a group*.  Surely, a
player's rating ought to drop when he loses a game, and ought to rise
when he wins.  The problem, with unrated players, is how much.

Assume: an unrated player's strength does not change appreciably during
        the provisional period.

(N.B. - you may not want to make this assumption0

Then - the USCF system requires that you first rate the UNRATED players
in a tournament, and then use their post-event ratings as their
pre-event ratings, for purposes of rating everyone else.  So, in the
extreme case where an unrated plays only one game against a rated
player, the rated player wins/loses the absolute minimum number of
rating points from that game.  Essentially, he wins/loses 0.
[assume the unrated player beats a 1600 established player.  His
provisional rating is 2000, and the 1600 player loses the same number of
points he would ordinarily lose by being defeated by a 2000-rated player
- for all intents and purposes, 0].  The unrated player gets a
provisional rating of 1600.  If he continues to play at 1600 strength,
then the rating points won/lost against other established players will
be correct.  Minor variations in performance result in rating points
being taken from some established players, and then re-distributed to
other established players.  

Some people are only convinced of this after actually crunching through
the numbers - so I'll make an offer.  If you will construct a "history"
[up to 21 games - broken up into tournaments of at least 3 rounds each]
for a new player, I will be happy to crunch the numbers and demonstrate
the effect of that history on both the unrated player, and all of his
opponents.  Feel free to construct as strange a history as you like -
but I reserve the right to comment on the likelihood of the history.  I
am confident that it will be difficult to construct a history which has
any appreciable "incorrect" effect on either an individual established
player, or on the established player pool as a whole.

>
>I don't think new players would find it difficult to find opponent
>willing to play them.

A potential problem with your proposes scheme is that many players do
not want to play, or do not take the games "seriously" if rating points
are not at stake.  The established player would literally have "nothing
to lose" and this might affect their strength.  But, this is probably a
minor nit.  For a system with the apparent constraints of ICS (single
game matches, rated game-by-game), I would agree that it would be
acceptable for individual opponents of unrated players to see no rating
change whatsoever.  Changing established ratings based on an "assigned"
provisional rating is simply wrong, unless the goal is to attract the
`average rating' to that value.  In that case, there isn't much point in
even distinguishing between `provisional' and `established' ratings -
except possibly to select an appropriate K, as FIDE does.

Notice that FIDE is different that ICS in that there is a certain
minimum competence required of new FIDE-rated players, and a certain
assurance that a new FIDE-rated player is reasonably close to that
minimum competence level.  Players of 900 strength do not enter
FIDE-rated tournaments, and players of 2900 strength who have never
competed in a FIDE tournament simply don't exist (well, no humans,
anyway...) 

-- 
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