Glicko Rating System

The Glicko rating system, invented by Mark Glickman in 1995 as an improvement on the Elo rating system, assesses player strength in zero-sum two-player games. Its key addition is ratings deviation (RD), which measures the accuracy of a rating, so a player rated 1500 with an RD of 50 is expected to have a real strength between 1402 and 1598. The Glicko-2 system adds rating volatility to reflect how erratic a player's performances are. Both systems are in the public domain and have been implemented on platforms including Lichess, Chess.com, and Dota 2.