TrueSkill

TrueSkill is a Bayesian skill rating system developed by Herbrich, Minka, and Graepel at Microsoft Research and introduced at NeurIPS 2006. It represents each player's skill as a Gaussian distribution parameterized by a mean (estimated skill) and a variance (uncertainty). After each match outcome, the system updates these distributions via approximate message passing, yielding a principled ranking that handles team games, draws, and partial observations in online settings.