K-FACTOR

***** K-Factor *****

The k-factor is a number in the formula used to calculate ratings.
It determines how many rating points you gain or lose in one game.
For example, if you beat someone with the same rating as you, on ICC
you will gain 16 rating points, and in FIDE you will gain only 7.5
rating points.  This is because the k-factor on ICC is 32, and the
k-factor in FIDE is 15 (for people with ratings below 2400).

Many people think that the larger k-factor on ICC is responsible for
the high blitz ratings of the top players on ICC (over 3300) compared
with the top FIDE ratings (2800).  This is not the reason.  The
k-factor only determines how quickly your rating moves towards the
level that you are performing at.  It does not determine what that
performance level is.  Here is a simple example to illustrate this
idea:

Suppose Joe and Fred are both rated 2200.  They play a 4-game match
and Joe wins 3-1.  A score of 3-1 is a performance 200 rating points
higher than your opponent's performance.  Joe's rating will go up,
and Fred's rating will go down, after the match.  If Joe and Fred keep
playing 4-game matches, and Joe wins every match 3-1, then eventually
Joe's rating will go up close to 2300, and Fred's rating will go
down close to 2100.  That's a 200-point difference in their ratings.
Even if they play hundreds of matches, Joe will never go above 2300
and Fred will never go below 2100.  This is completely independent of
the k-factor used to calculate ratings.  The final "goal" rating 
(2300 for Joe and 2100 for Fred) has nothing to do with the k-factor.

The k-factor determines how fast Joe will approach 2300 and how fast
Fred will approach 2100 in this series of matches.  For example, on
ICC it might take only 5 matches for Joe to reach 2290, but in FIDE
it might take 10 matches.

So you see that the k-factor is not responsible for the high ICC
blitz ratings.  I am not a statistician, and cannot prove the cause
of the high ratings.  But one possible reason is that in ICC blitz
you can choose your opponent.  Then it is possible for high-rated
players to:

1) Choose computers that they know they can beat with a certain strategy.
2) Choose opponents that they think are over-rated.
3) Avoid playing strong players who are rated several hundred points
below them.  For example, if a 3300 player were forced to play all
the ICC GMs with 2800 ratings, his rating would probably drop,
because he would have to score around 95% to maintain his 3300!

This idea is supported by the results of the new 5-minute rating
category on ICC, in which you cannot choose your opponent.  The
top ratings in that category are only 2500.

Another possible reason for the larger range of ICC blitz ratings
is that the range of ratings in a rating system may increase as more
games are played.  On ICC there are over 4 million games played each
year, many times more than the number of games rated by FIDE.

[POTZY, 10/18/2002]

See also: ratings, five-minute, best