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Subject: Re: Performance rating calculation

Author: Peter Fendrich

Date: 17:30:29 06/03/04

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On June 03, 2004 at 12:46:39, Dan Wulff wrote:

>Hi Peter!
>
>On June 02, 2004 at 19:04:15, Peter Fendrich wrote:
>
>>forget about performance rating (and your statement about 16 points is wrong...)
>
>Wrong, how ??? The formula for Expected score is:
>
>1/(1+(diff/400)) which will always give a number less than 1.
>
>to calculate the win/loss you need (Score-Expected score)*16 for master players
>(*32 for lower ratings). How should that ever be more than 16 points, master
>games ??
>
>Greetings
>
>Dan Wulff
>(The Gandalf Team)

Hello Dan,
Yes I agree, you're right, but the values 16 and 32 are selected more or less by
random...
I don't think that performance rating is the right way to go. It is not intended
to be used for one game only.
IMO it's clearly better to use the expected score based on the rating diff.

For instance if the rating diff is 100 the expected score is 0.64 for the higer
rated player. I can send you a table with expected scores depending on the
rating difference if you want to. I think that you could use that figure instead
of rating points.

Now, with the expected score 0.64 you can translate it to an ELO
increment/decrement that makes the ELO difference to be kept to 100 when a lot
of games are played. 64% of n (many) games should keep the ratings unchanged for
these two players.
In the table (from the link I gave you) you will find that the higher rated
player earns 12 points per winning game. Suppose that we have a 100 game match
with the expected result 64-36. 64*12 - 36*20 should be 0 but it's not. That's
strange, I thought that the LASK system should fit! Well, if you want to
translate to ELO points it's probably better to adjust the table to fit your own
purpose. It's not a very hard task with the expected score.

/Peter



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