Elo Rating Algorithm is widely used rating algorithm that is used to rank players in many competitive games. Players with higher ELO rating have a higher probability of winning a game than a player with lower ELO rating. After each game, ELO rating of players is updated. If a player with higher ELO rating wins, only a few points are transferred from the lower rated player. However if lower rated player wins, then transferred points from a higher rated player are far greater.
P1: Probability of winning of player with rating2
P2: Probability of winning of player with rating1.
P1 = 1 / (1 + 10 * EE(rating1 – rating2) / rating separation value)
P2 = 1 / (1 + 10 * EE(rating2 – rating1) / rating separation value)
And P1 + P2 = 100%
The rating of player is updated using the formula given below :
rating1 = rating1 + K*(Actual Score – Expected score);
rating2 = rating2 + K*(Actual Score – Expected score);
In most of the games, “Actual Score” is either 0 or 1 means player either wins or loose. K is a constant. If K is of a lower value, then the rating is changed by a small fraction but if K is of a higher value, then the changes in the rating are significant. Different organizations set a different value of K.