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Topic: Rating - How calculate it?

Author

Message

rbivanov

How can we calculate, correctly, the rating after a match between two players with established ratings? In the Help session we have:

Established Ratings

For players that have played 25 or more games the following formulas are used to compute their rating:

new rating = old rating + 0.04 * (rating difference) + 16 (for the winner)
new rating = old rating + 0.04 * (rating difference) - 16 (for the loser)
new rating = old rating + 0.04 * (rating difference) (in case of a draw)

Well, recently I lost a match against a player who had rating 2223 and, after the match, our ratings had become:

Me: 1558 -> 1556
Him: 2223 -> 2224

Second the calculation formula, in Help session, our ratings should be:

Me = 1558 + 0.04*(2223 - 1558) - 16 = 1569
Him = 2223 + 0.04*(2223 - 1558) + 16 = 2266

So, why this difference? Was there exceptions of the calculate rule? Why those exceptions aren't in Help session?

In Help, there is a link to US Chess Federation (http://www.uschess.org/cc/ccratefl.php), but it didn't work here (404 error).

Thanks for help!

miguel

I just fixed the link to the US Chess ratings explanation page, they moved the page to a different location.

The coefficient changes when ratings are over 2100, that is what is missing in your computation. This is explained in the US Chess page.

Miguel

rbivanov

Thanks, Miguel.

If you have the new link, I appreciate

miguel

http://main.uschess.org/content/view/7520/393/

rbivanov

Thanks, Miguel!

rbivanov

Miguel,

In the another topic (but in Portuguese), andreavb contributed with some information that could be implemented in the Queen Alice Help session.

Where the rating rules are explained, in Help session, may figure the following equation:

Rating Difference = (Opponent's Rating) - (Your Rating)

Certainly, this equation will answer many questions about the rating calculation, because the variable "Rating Difference", actually, isn't explained how to calculate it. The signal can be plus or minus, changing the final result.

Greetings!