How are rank changes calculated?!?

[zdepthcharge]

I played a game today when I was ranked 244 against someone who was ranked 496. They won by about 8 points. Their rank went to 500 and mine went to 239.

O.K.

I just played a game against someone ranked 10 points below me and I lost the game 208 to 206. My rank went down 10 points and theirs went up 10 points.

How are rank changes calculated?

[yoyote]

Hello,
I think that the game result doesn't count.
You can lose 300-150 or 201-202, it's the same calcul : only the number of games played, your rank and the opponent's rank are used to calculate your new ELO, and the new ELO of your opponent.
For all the games.

[Liallan]

This is not directly related to a given game; it's about how ELO is calculated and yoyote is correct that it's not related to the actual scores you get in the game, only whether you win or lose. The only relationship to Stone Age itself is where you end up ranking is based on the ELO you have and how that compares with everyone else's ELO on that same game. (The amount of luck in a game can affect it too.) And your ELO isn't your rank - I mean your rank like 131st place of all players.

I would make a suggestion that you go to Discussions and Suggestions, and do a search on ELO and look for the more recent stuff, as they changed some things a few months back. If you're not finding anything that really gives you a satisfactory answer, then I'd ask about it in the Discussion forum. The people who may be able to best answer questions might not even know Stone Age or be reading this.

I know Stone Age but don't know a lot about ELO. The one thing I can tell you is that if you are higher ranked than someone else, you are supposed to win, and if you lose then it's going to affect you more than if you lose to someone who is higher than you. If you think about that, it makes total sense. But that's all else being equal, and everything else generally isn't equal so you can't make it quite that simple. But you also have to realize the actual score in the game is not taken into account. While losing by 1 point might seem unfair because you'll lose the same amount of ELO, you'll make up for it when you lose by 40 points and don't lose any extra for that. (And vice versa when you win.)

[Jest Phulin]

Well, the quick and dirty... (If you want exact formuae, consult the discussions forums) [Actually, strike "quick." I tend to over-explain... ]

There are two numbers you seem to refer to, rank and ELO. These numbers are related, but are quite different. Rereading the original post, I think zdepthcharge used the word "rank" when discussing ELO.

ELO can be thought of as a probability of a person winning a particular game. If two players have the same ELO, they should each win half the time. It doesn't matter if they both have a high ELO (both experts) or both have a low ELO (both apprentices) -- their skill levels are the same, they are equally matched. However, when ELO is different, the player with the higher ELO should have a higher probability of winning. I think the numbers boil down to that if the difference in ELO is 100, the stronger player is expected to win 2 out of every 3 matches, and if the difference is 200, they are expected to win 3 out of every 4 matches. This leads to the titles "apprentice," "good," "expert," etc.

ELO was designed for chess, and adapted for many other games. With that, there are some issues. First, chess does not have a score: it is either a win or a loss (well, OK, it could also be a tie). With that, for games like Stone Age, it does not matter if the win is 50-1 or 101-100; both scores calculate as a win. Also note that chess is a strictly 2-player game. BGA has tweaked it so that in multi-player games, the calculation is done as if several simultaneous 2-player games were done at once. IE, if the final positions of the players were A, B, C, D, the ELO would be calculated as A wins against B,C,D -- B loses to A, but wins against C, D -- C looses to A and B, but wins against D, and D has 3 losses.
ELO, after several games, is a zero-sum point transfer. ELO gained by the winner is equal to ELO lost by the looser. But, again, this is after several games. While the system is trying to determine what a new player's true ELO is, it may give or remove more points with them.
Going back to the probability of winning, the point transfer is greater for a lower ELO to win against a higher ELO than for the higher ELO winning against a lower. IE, if someone who is expected to win 3 out of every 4 matches 3 of 4, it's not an accomplishment. But, if someone who is expected to win only 1 out of 4 wins 2 of 4, it is an accomplishment. (Fine, it really should be 30 out of 40 and 20 out of 40, but whatever...) This is why the 244 v 496 match transferred 4-5 points (rounding), while the 10-point difference match transferred 10 points.

Now, as to rank.
Rank is how a player's ELO measures against all other players' ELO on the site. The person with the highest ELO is ranked first, second highest ELO is ranked second, etc. Take all players with an ELO on this site, put them in a list, and sort by ELO -- you get the ranking. It doesn't matter if 20th place has an ELO 10 points or 30 points higher than 21st place, it is still 1 place higher.

Hope that helped.
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Edit -- the most effective search to find details is probably "k factor" or "k-factor," rather than "ELO." The k-factor is used in the calculations, so posts with that generally are the formulae, or answered with the formulae.