ELO system in BGA has bug or is not fer

[PiotrP2]

Usually on BGA I play Carcassone game.
When I win i get only few points. When lose game, than i lose a lot points.
Sometimes to much. Example
https://5.boardgamearena.com/5/carcasso ... e=51309224
Bad game for me.
I was last.
Before game 3-th person have similar points to me (he 452, me 456)
After game he lost 12 points.
Me 26 poinst!.
It means that my lost to first 2 persons should also be 12 points.
My lost to 3-th person looks as 14 points. But why ? We are have the same level.
It is notunderstendable.

I saw in FAQ rule: K x (W - p(D))
You send us to Wikipedia, but i dont see in wikipedia any explanation to p(D).
Maybe it is the reason why i lost so many points.

OR maybe there is a BUG.

It makes me that I hate ELO system used in BGA.
It is NOT FER.

I feel bad after all lose, because i know that i have to win 3 times to win the same number of point which i lost in only 1 game.

PLEASE FIX it. Change notunderstendable p(D) or GIVE at the beginning information that playing in this you can win/lose x, y, z points (depending on place). If i know that i can lost 26 points I wouldnt play. Because risk is too high. Games on PGA it is not chess. In this games we have big random element.

[RicardoRix]

You lost to 3 other people, the guy in 3rd place lost to only 2 people and beat 1 person - that is essentially how the ELO calculation works as a series of 1v1 matches.

If you finished 3rd and the other ELO 400 finished 4th, then the minus points would have been near identical, there is no extra punishment specific to you.

The higher your ELO rating the more you have to lose to those with lower ELO. If you don't like that situation then seek out players with >400 ELO to reverse the situation to your liking.

[Tulivuori]

It would be nice if the FAQ was correct though. Being last in 4 player game actually seems to make you lose less points than 3 losses in 1 vs 1 games, at least when K factor is 20.

[RicardoRix]

Forgot to say:
In the results page, you can hover your ELO rating and it will display the calculation.

[Tulivuori]

Calculation fails in simple addition though.

[Schtitn]

Calculation fails in simple addition though.

+1
I say it for long time now, additions are just mysterious!!!!

p(D) = probability of the result you get against your opponent
for example, against an opponent with 0 elo, probability of winning is 99% so you get W x (1 - 0,99) elo if you win.
values for p(D) are given by wikipedia considering the difference between the elo of players

[asd123321]

What is poor is that it is weighted way to much for a few recent games and the fact that you have won a large per cent of 540 is not so significant. It should be changed a lot more that the more you have played, the less the last game would change it. They do some of that but not enough.

[Silene]

Piotr, your calculation is just not correct.

Should be like this:

You and neko lost 19 points for losing to player 1 and 2.
neko gained 7 points for beating you
you lost 7 points for losing to neko

That's how you add up at -12 and -26. As you can see your loss to player 1+2 each lost more elo than your loss against player 3. As it should be since they had lower elo before the game.

[Silene]

I think that playing multiplayer- game should have much less effect on your elo in general. I don't think it should be calculated in the same way as 3 single games. Maybe it is already reduced a bit, but I think it should be more like:

Devide the calculated ELO-change by the number of your opponents!
So I think if there's already some reduction in place (maybe that's why the numbers do not add up?) - it's just not enough.

The reasons:

• It is out of your control wether your opponents target you as an enemy or play in favour of you. That means there is more of luck involved than in 1 on 1. I think usually luck-heavier games lead to a lower elo-change in general (correct me if I'm wrong). This should be reflected in 3+ player games also.
• you played only 1 game after all. Should lead to similar ELO-variation as a 1 on 1.

For team games, there should be individual solutions. Winning as survivors in Not Alone is not a tie with your teammates. And the creature did not lose to 4 other players but lost to one other team (with elo = average of the 4 players).
So maybe devide not by number of players but by number of opposing parties and do not calculate anything against your teammates.

[might cause problems especially on Not Alone because elo-change is not symmetrical then. this would be ok if the propability for survivors to win is the same as for the beast. I think that's probably not the case so this would cause elo-inflation or deflation. maybe some factor between beast/survivor elo-change is in need, to balance that]

(fun fact: on solo-games you'll have to devide by zero. That's why thermophyles-elo is bugged )

[Tulivuori]

Devide the calculated ELO-change by the number of your opponents!

Since no one bothers to explain how ELO in multiplayer games actually work and why it's wrong in the FAQ, I needed to reverse engineer it. It seems that to some extent, this is actually happening. If your K factor is 20, it gets lowered based on number of players. In 2 player game it is 20, in 3 player game it is 15 and in bigger games it is 40/number of opponents, so a multiplayer game with at least 4 players has kind of the same effect as 2 individual matches would have. If your K factor is over 20, this doesn't happen.

I don't undertstand wy this hasn't been documented to FAQ, and why mathematically incapable people are directed to look the p(D) from wikipedia article which is full of chess and mathematics (it is well explained there, but may not be that easy to figure out where to look).