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Subject: Re: A theory of ratings drift for the SSDF

Author: Sune Fischer

Date: 03:27:29 04/12/02

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On April 12, 2002 at 00:16:35, Robert Hyatt wrote:

>It _must_ affect both the rating of other players, and the "spread" to some
>small degree.  A drop of water hitting the pond changes the depth everywhere
>as the ripples propogate around and reflect...  Remember that the spread between
>two player's ratings is a statistical average of how the two players do against
>all other players in the pool.  Adding a new player can change this.  IE a
>player joined our local club back in 1970, and he was rated 300 points above
>me, yet I won the majority of games against him because our "styles" gave me
>an advantage...  that obviously changed the spread between me and other players
>in the club, yet I did no better (or worse) against them after the new player
>arrived...
>
>

Well as a short term effect this will send ripples up and down the ranks, but
when they have decayed and you have gone back to playing games with the other
players, you will share some of your won rating with them, or they will also
beat the new guy.
The lasting effect is just an indication of the usual uncertainties that applies
to ratings, i.e. you where actually stronger than you thought if only you were
able to increase your rating.

The overall spread can't really change if the same formula is used, the pool
will expand or subtract to fit the formula eventually.

-S.



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