ELO calculations for Azul

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MrBeardy
Posts: 141
Joined: 28 January 2022, 11:23

ELO calculations for Azul

Post by MrBeardy »

can someone explain how ELO work for this game as so far as I can tell it seems to behave differently to other games on BGA
at the end of my games I seem to get hammered on ELO if I lose. Take this game for example:

https://boardgamearena.com/1/azul?table=244584750

We start of within 10 ELO apart me on 135, the other player on 144. I lose and get deducted 19 and they gain 10. In other games the deduction and gain would be similar, within 1 or 2 (eg +9/-10) for players with similar ELO, and typically favouring the lower ranked player.

Similarly in this game: https://boardgamearena.com/table?table=244391764

He starts on 231 and me on 133. He wins and gets +7, I lose (as expected) and I get hit with -22. It just seems a bit disproportionate.
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thoun
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Joined: 10 December 2020, 22:25

Re: ELO calculations for Azul

Post by thoun »

I can't explain how it works exactly, what I can tell it's that is the same algorithm for all games. Azul doesn't handle Elo calculation, Bga does, according to game ranking given by Azul scoring
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Silene
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Joined: 23 October 2013, 17:50

Re: ELO calculations for Azul

Post by Silene »

You have a higher K-factor because you haven't played the game very often yet. It's shown in mouse-over on the ELO-change.

In 2-player game, ELO win/loss is symmetrical. But the K-factor applies after this initial calculation. Players with fewer games get added/reduced their ELO more. The idea of this is that ELO is supposed to be a measure of skill. Everyone starts at 0 ELO but maybe you already have some skill --> so you have a couple of games to get to a more accurate estimate of your supposed ELO quicker.

I don't know exactly what number of games gives you what K-factor. Maybe someone else can add that here.
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Lumin_S
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Joined: 09 October 2018, 00:51

Re: ELO calculations for Azul

Post by Lumin_S »

Here are the steps for Elo calculation:

1) Based on starting Elo, BGA decides what % chance you have to win. On the first table you linked it was 51% vs 49%, and on the second it was 64% vs 36%. I can't give you the exact math of "why" these numbers, but if you look up how Elo systems generally calculate this, you'll get a good idea.

2) BGA assigns you a K-factor which is based on how many times you've played that specific game. Everyone's K-factor starts high on their first few plays and sinks to 20 after you've played some games (I think it's roughly 20 games to get the K down to 20.)

3) Once the game ends, the Elo change is calculated by multiplying the (opposite probability of the outcome) by (the K-factor). For example in the game you linked where the Elo change was +7.25 vs -21.75, the outcome was 64% likely, so (100% - 64%) times (K-factor) was the Elo change for both players.
MrBeardy
Posts: 141
Joined: 28 January 2022, 11:23

Re: ELO calculations for Azul

Post by MrBeardy »

Thanks for the replies. In this game https://boardgamearena.com/7/azul?table=244636254 the other player had over 300 ELO and I was 159 so he's approx double my rating and has a 70% chance of winning. I won and got +14 and they got -14 which again doesn't seem right. It's like I'm getting fewer points when I win even against significantly better ranked players and lose more points for a loss than I gain for a win no matter who I lose to.

If it was to do with K factor before we each had the same K factor (20) for this game. Does that mean this silliness is now over and normal weightings will apply going forwards?

trying to apply the maths as lumin's post:

70% x K=20 = +/-14 points. which is what we each got. If I'd have lost it would have been 30% x K=20 = +/-6 points?
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dschingis27
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Joined: 27 June 2015, 18:30

Re: ELO calculations for Azul

Post by dschingis27 »

MrBeardy wrote: 22 February 2022, 19:27 Thanks for the replies. In this game https://boardgamearena.com/7/azul?table=244636254 the other player had over 300 ELO and I was 159 so he's approx double my rating and has a 70% chance of winning. I won and got +14 and they got -14 which again doesn't seem right. It's like I'm getting fewer points when I win even against significantly better ranked players and lose more points for a loss than I gain for a win no matter who I lose to.

If it was to do with K factor before we each had the same K factor (20) for this game. Does that mean this silliness is now over and normal weightings will apply going forwards?
Yes! Your last 3 games were your games 21-23, so now you will have K=20 forever. In your 18th game, this one, you still had a K factor of 40 and took advantage of it, because you gained more points than your opponent lost. So the system is not targeted against you. ;-) https://boardgamearena.com/table?table=244597333
MrBeardy wrote: 22 February 2022, 19:27 trying to apply the maths as lumin's post:

70% x K=20 = +/-14 points. which is what we each got. If I'd have lost it would have been 30% x K=20 = +/-6 points?
Exactly! When you loose against a player with higher Elo, you will loose less points than the points you gain when you win against that player. Rule of thumb: IF less expected outcome occurs THEN stronger Elo change will happen, IF more expected outcome occurs THEN smaller Elo change will happen.
MrBeardy
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Joined: 28 January 2022, 11:23

Re: ELO calculations for Azul

Post by MrBeardy »

thanks all, that's really helpful. Much appreciated. :mrgreen:
tony97
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Joined: 16 January 2022, 20:13

Re: ELO calculations for Azul

Post by tony97 »

read something similar for another game, maybe it helps: https://boardgamearena.com/forum/viewto ... 91&t=24354 ...the last post
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