When you hover your mouse over a player in the "list of tables", you will be shown the player's Elo rating, provided they have been ranked.
Wikipedia does a pretty good job of explaining how Elo ratings are computed.. There, an example is given of someone playing in a 5-round tournament:
Suppose Player A has a rating of 1613, and plays in a five-round tournament. He or she loses to a player rated 1609, draws with a player rated 1477, defeats a player rated 1388, defeats a player rated 1586, and loses to a player rated 1720. The player's actual score is (0 + 0.5 + 1 + 1 + 0) = 2.5. The expected score, calculated according to the formula above, was (0.506 + 0.686 + 0.785 + 0.539 + 0.351) = 2.867. Therefore the player's new rating is (1613 + 32 * (2.5 - 2.867)) = 1601, assuming that a K-factor of 32 is used.At World of Card Games, the process is very similar. The performance of each player against their opponents at the table is treated as a "round" in the tournament described above. Here's an example for a game of Spades.
Suppose there are 4 players: A, B, C, and D, with ratings 1512, 1562, 1484, and 1417, respectively. A and C are teammates, while B and D are their opposing teammates. The "expected" score for player A competing against player B is computed as 1 / ( 1 + 10
According to Elo, a player's actual score is given by 1 for a win, 0.5 for a draw, and 0 for a loss. If player A won against player B, then the actual score for player A would be 1.
In a Spades game, performance for an individual player is evaluated against 2 opposing players. If players A and C won over B and D, then player A's "actual" score is Sa = 1 + 1 = 2. The expected score for player A is the sum of [1 / ( 1 + 10
Player A's new Elo rating is computed according to the formula given in Wikipedia: Ra
A similar computation is made for players B, C, and D. Each player's Elo rating is computed using their own Elo rating and the Elo rating of their two opponents.
Please check out the Wikipedia article for more details if you are curious. Obviously, there are flaws to applying a rating system that was developed for chess to a card game like Spades. Most game sites use this system, and I have followed suit.
In Hearts, your Elo rating suffers more if you quit a game because you automatically lose to all remaining players. In Spades this is not done. For one, rating a player against their teammate when they quit seems just too bizarre. It would put the player in a match against three other players, while the opponents would be matched against just two, and that would lead to a skewing of the ratings. Also, I've had a few protests about the way that a player's Elo is affected when quitting a Hearts game. Some people say that it is enough that they lose the game automatically, and they should not take a loss to all remaining players. So the Elo ratings in Spades do not place an additional penalty on a quitter. It's an experiment to see if a heavier penalty is needed for quitting or not.
Suppose 4 players with an Elo rating of 1500 start a ranked Spades game. Mary and Sue are teamed up against John and Peter. Halfway through the game, Peter realizes he must rush off to pick up his kids from school, so he apologizes and quits the game by clicking the "leave table" link. His Elo rating is immediately changed from 1500 to 1470, and he is banned from ranked play for 2 hours. The new Elo rating is computed from the formula Ra
The Elo ratings of all remaining players are unaffected until the game is finished. Now suppose that John, whose partner quit, goes on to win the game. The resulting Elo ratings of the remaining players are computed with Mary and Sue winning against Peter, but losing to John, so their Elo ratings actually remain at 1500. As an example, Mary "won" over Peter (because he quit), and lost to John, so Mary's Sa = 1 + 0 = 1. Mary's Ea is also 1. So the formula Ra