Board Game Arena

Hello,

after last bang game I spotted strange ELO calculation. We won as outlaws on BANG game. In game results I spotted that my teammate with significantly higher ELO got bigger ELO boost than others for winning a game.
Attaching screen.

Can anyone explain how is ELO calculated and why this occasion happened ?

Thank you.

He played less than 20 games total, so his K-factor is higher, which means he will win more points in case he's winning the game and lose more in case he's losing the game. But apparently the mouse-over on the elo-calculation doesn't show a different k-factor. Seems to be a bug on the mouse-over display. However the calculated score is probably right even if the mouseover doesn't show it correctly.

But in general elo-calculation is broken for team-games - they shouldn't calculate a tie between partners that would always win/lose together. But that's not the origin of the effect that you're obverving here.

For the record, below are the detailed calculations as displayed by BGA

Imperator Cade earned 20.75 ELO but the individual values total to 24.9
You earned 19.2 ELO but your values total 46.06

Below is the formula used by BGA:

BGA FAQ wrote:The easiest situation is a 2 player game. You will gain a number of ELO points equal to K x (W - p(D)) where:

• W is the result of the game: 1 for a victory, 0 for a defeat, 0.5 for a tie.
• D is the difference of ELO between you and your opponent.
• p(D) is the probability of victory considering the previous difference (see Wikipedia for details).
• K, the 'elasticity factor,' has a value that depends on the number of games you have played: 60 for your first 10 games, 40 between your 11th and 20th games, 20 for your 21st onwards.

Some more details and specific cases:

• On your very first game, you always win at least 1 ELO point, even if you lose the game.
• Until you reach 100 ELO (beginner), you can never lose ELO points. After that you can never go back below 100 ELO.
• When you play with more than 1 opponent, we consider that you win against each opponent who scores lower than you during this game, and lose against each opponent who scores higher than you. For example, if you place 2nd in a 4 player game, you gain ELO points as if you won against the 3rd and 4th players, and lost against the 1st.

ELO was designed as a 1 vs. 1 calculation. It really wasn't intended for multiplayer (n > 2) situations and in some scenarios it is completely nonsensical to use it.

Meeplelowda wrote: ↑08 January 2023, 22:50 ELO was designed as a 1 vs. 1 calculation. It really wasn't intended for multiplayer (n > 2) situations and in some scenarios it is completely nonsensical to use it.

1 on 1 combinatorial games, to be exact.
Better than nothing though.