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How does lichess calculate tournament performance?

Asked by swohl19
Activity Viewed 846 times, last updated
1
Just wondering because it seems to vary a lot from each tournament I play in.
One answer
3
Answered by milliways
LDog11 commented :
I tried doing the calculation; I had a draw and it looks like they threw that score out, but even with that adjustment I still ended up with a six point discrepancy.
Toadofsky commented :
I agree, it's not 100% the same as Elo or Glicko.
lollycopter commented :
> private val DIFF = 500

Unlike the magic 400 number that's in Wikipedia, Lichess uses 500.

Therefore formula is:
[SumOfOpponentRatings + 500 * (Wins - Losses)] / Games

Remember that (Wins - Losses) can give a negative value, so if you win 1 and lose 3 in a tournament, basically subtract 1000 (i.e., 500 - 1500) from the sum of your opponents' ratings before dividing by the total number of games played.

Example, PR from 1 win and 3 losses with 4 opponents all rated 1500 = [1500 + 1500 + 1500 + 500 * (1 - 3)] / 4 = 875
lollycopter commented :
> "I tried doing the calculation; I had a draw and it looks like they threw that score out, but even with that adjustment I still ended up with a six point discrepancy."

I think I've figured it out -nothing is being thrown out (draws are a game added to the denominator, but they neither add nor subtract 500 to the numerator).

What's probably happening is that the final game you play in a Tournament ends after the "hourly" window for the tournament. That final game gets added into the performance rating calculations, but it *won't* appear in the neat little game table.

If you play overtime, try tallying up the results from your own profile page games list, rather than the little table on the tournament page (which will always omit the game that finishes after the cutoff time.

What this essentially means is that games finishing after the cutoff still matter in a sense and will reflect in the performance rating, even if they won't add points to the tally.

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