Page 1 of 2
Why does a tie result in a loss/gain of ELO?
Posted: 09 February 2022, 16:58
by truthhungry
I've noticed this a few times but it finally caused me to ask the question...why in the world would a tie result in a loss/gain of ELO?
Re: Why does a tie result in a loss/gain of ELO?
Posted: 09 February 2022, 17:02
by Silene
ELO is a number to measure your strength. So if your opponnent has a much higher ELO than you do, but you manage to tie with them, it suggests that you're closer in strength than your previous ELO showed. So higher player gets down a bit, lower player gets up a bit to reflect that new information about your (and your opponent's) strength. But not nearly as much as if the lower player had beaten the stronger one.
Re: Why does a tie result in a loss/gain of ELO?
Posted: 09 February 2022, 17:09
by buv3x
Rating change after a game is calculated as D = K*(R-E).
K is a predetermined constant, so it just scales the difference.
R is an actual result, with usually victory=1, tie=0.5, loss=0.
E is an expected result, your win probability based on players' ELO. It's a value from 0 to 1.
When ELO is equal for both players E=0.5 (which is the same way of saying that win probability is 50% for both players). Therefore D=0.
However if ELO differs and you win probablity is calculated as, say, 66%, E=0.66, then in case of a tie your D = K*(0.5 - 0.66) = K*(-0.16), therefore your rating drops.
Re: Why does a tie result in a loss/gain of ELO?
Posted: 09 February 2022, 18:01
by FSKFSK
The way ELO works, each player contributes rating points to the "pot". The player with the higher rating contributes more. The winner gets the "pot".
If you tie, the pot is split evenly, which means the lower ranked player increases their rating and the higher ranked player decreases their rating.
(If you are a new player at a game, it works a little differently, because the new player has a bigger K factor.)
Re: Why does a tie result in a loss/gain of ELO?
Posted: 09 February 2022, 18:53
by robinzig
FSKFSK wrote: ↑09 February 2022, 18:01
The way ELO works, each player contributes rating points to the "pot". The player with the higher rating contributes more. The winner gets the "pot".
I don't see how this is true, and it may confuse people so I feel I have to call it out - no offence intended.
You make it sound like there is a single "pot" of rating points that the winner gains and the loser loses - but that is not the case. If a very strong (= high ELO) player plays a much weaker (= lower ELO) one, then if the strong player wins the game they gain only a very small amount of ELO (and the loser loses the same amount). Whereas if the weak player wins, they gain - and the strong player loses - a much larger amount. This reflects the fact that the win of the strong player is "expected" so there is not much change in rating, whereas the former result is unexpected and suggests the pre-existing ELO ratings are wrong, hence there is a large "correction factor".
Re: Why does a tie result in a loss/gain of ELO?
Posted: 09 February 2022, 20:12
by FSKFSK
No, this is exactly how ELO works.
Example involving a much higher rated player:
The higher rated player contributes 18 to the pot, and the lower rated player contributes 2 to the pot.
If the higher rated player wins, they get +2 (20 minus their contribution of 18). If the lower rated player wins, they get +18 (20 minus their contribution of 2)
If it is a tie, the pot is divided equally, so the higher rated player would get -8 and the lower rated player gets +8.
If one player is new, there is a "K factor" adjustment, where their gain or loss is multiplied by the K factor.
For multiplayer games, it is treated as a head-to-headmatch involving each player, but with a hidden K-factor adjustment based on player count to decrease the total gain. (So winning a 3 player game is less of an increase than winning 2 head-to-head games against each oppponent.)
Re: Why does a tie result in a loss/gain of ELO?
Posted: 09 February 2022, 20:32
by robinzig
FSKFSK wrote: ↑09 February 2022, 20:12
No, this is exactly how ELO works.
Example involving a much higher rated player:
The higher rated player contributes 18 to the pot, and the lower rated player contributes 2 to the pot.
If the higher rated player wins, they get +2 (20 minus their contribution of 18). If the lower rated player wins, they get +18 (20 minus their contribution of 2)
If it is a tie, the pot is divided equally, so the higher rated player would get -8 and the lower rated player gets +8.
If one player is new, there is a "K factor" adjustment, where their gain or loss is multiplied by the K factor.
For multiplayer games, it is treated as a head-to-headmatch involving each player, but with a hidden K-factor adjustment based on player count to decrease the total gain. (So winning a 3 player game is less of an increase than winning 2 head-to-head games against each oppponent.)
Thanks, I see you are right but I don't feel bad for having misunderstood and clarified. The crucial bit that wasn't explicit from your original post was that each player *loses* their "contribution" to the pot before (if they win) gaining the whole pot back - therefore profiting by the other's contribution.
Re: Why does a tie result in a loss/gain of ELO?
Posted: 11 February 2022, 02:12
by diamant
truthhungry wrote: ↑09 February 2022, 16:58
I've noticed this a few times but it finally caused me to ask the question...why in the world would a tie result in a loss/gain of ELO?
ELO points are normally only earned or lost after a competition between 2 players. When a tie occurs between 2 players of unequal strength, the stronger player loses ELO points, and the weaker wins some, because the strong player is more likely to prevail over the weaker.
On the other hand, performing an ELO points calculation according to the same principle in the absence of competition is nonsense for me. For example, when 2 players are tied because they belong to the same team, or when the result of a game has been neutralized and all players are tied except the loser who left the game for one reason or another. No one should be able to lose points in the team of winners, because it is usually the strongest players who contribute to the team winning.
Re: Why does a tie result in a loss/gain of ELO?
Posted: 11 February 2022, 03:28
by All7Pangaea
This makes a lot of sense. However in a partner game, could there be an option where since the partners by default will tie that they do not exchange elo.
Re: Why does a tie result in a loss/gain of ELO?
Posted: 11 February 2022, 04:24
by Cheery Dog
ELO is just broken for team games. Don't worry about it.