Author: Christophe Theron
Date: 12:08:55 03/17/04
Go up one level in this thread
On March 17, 2004 at 14:11:35, Uri Blass wrote:
>On March 17, 2004 at 13:52:55, Christophe Theron wrote:
>
>>On March 17, 2004 at 12:35:41, Uri Blass wrote:
>>
>>>On March 17, 2004 at 11:43:12, Anson T J wrote:
>>>
>>>>On March 17, 2004 at 10:40:30, Bigler David wrote:
>>>>
>>>>>Hi,
>>>>>
>>>>>Shredder 8 performed 82 ELO point better than Junior 8
>>>>>Junior 8 performed 82 ELO point better than Shredder 7.04
>>>>>
>>>>>So Shredder 8 performed 164 ELO better than Shredder 7.04
>>>>>
>>>>>rgds
>>>>
>>>>I see, I thought when it was -41 / +41 that A was 41 weaker than b and b was 41
>>>>stronger than a. Not that a was 82 weaker and b was 82 stronger. Perhaps you are
>>>>correct. thx
>>>
>>>56% is less than 50 elo difference based on fast calculation.
>>>
>>>If the result is 56-44 then I get the following difference in rating
>>>
>>>(56-44)/100*400=48 so my calculation give 48 elo.
>>>
>>>
>>>The formula that I use is only approximation to the real formula so I guess that
>>>41 is correct and not 82.
>>>
>>>Uri
>>
>>
>>
>>There is a simpler formula that is easy to remember.
>>
>>1) take the winning percentage of the winner
>>2) if it is above 80% stop here (the formula below does not apply)
>>3) subtract 50 from the winning percentage
>>4) multiply by 7
>>5) the result is the elo difference between the two
>
>The formula that I use is equivalent to doing the same as you do but multiplying
>it by 8 instead of 7.
Someone at the Israeli Chess Federation screwed up and I guess that now they are
forced to keep this formula for reasons that have more to do with
historical/political reasons than mathematical ones! :)
I think my formula is more accurate. And actually it's not _my_ formula. I have
found it somewhere, but I do not remember where.
The real elo formula has the interesting property to be close to linear in the
20%-80% winning percentage range, hence the 80% validity limit.
For computer chess, where top opponents are often very close in strength, the
formula is reven more reliable. I think it has a +/-1 elo point margin of error
in the 40%-60% range. Not bad for such a simple formula.
Christophe
>Maybe your formula give better approximation but the formula that is equivalent
>to multiplying by 8 is used by the israeli chess federation when they calculate
>performance of new players in order to give them initial rating(it is only for
>part of the players and part of the players get initial rating 1350).
>
>Usually the players who get initial rating based on performance are players with
>experience from tournaments in other countries and it is not their first
>tournament.
>
>Uri
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