TrueSkill is a skill-based ranking system developed by
Microsoft
Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...
for use with video game matchmaking on the
Xbox network. Unlike the popular
Elo rating system
The Elo rating system is a method for calculating the relative skill levels of players in zero-sum games such as chess or esports. It is named after its creator Arpad Elo, a Hungarian-American chess master and physics professor.
The Elo system wa ...
, which was initially designed for
chess
Chess is a board game for two players. It is an abstract strategy game that involves Perfect information, no hidden information and no elements of game of chance, chance. It is played on a square chessboard, board consisting of 64 squares arran ...
, TrueSkill is designed to support games with more than two players.
In 2018, Microsoft published details about an extended version of TrueSkill, named TrueSkill2.
It is based on a
Thurstonian model with a Gaussian score distribution. It does not satisfy
Luce's Choice Axiom.
Calculation
A player's skill is represented as a
normal distribution
In probability theory and statistics, a normal distribution or Gaussian distribution is a type of continuous probability distribution for a real-valued random variable. The general form of its probability density function is
f(x) = \frac ...
characterized by a mean value of
(mu, representing perceived skill) and a variance of
(sigma, representing how "unconfident" the system is in the player's
value).
As such
can be interpreted as the probability that the player's "true" skill is
.
On Xbox Live, players start with
and
;
always increases after a win and always decreases after a loss. The extent of actual updates depends on each player's
and on how "surprising" the outcome is to the system. Unbalanced games, for example, result in either negligible updates when the favorite wins, or huge updates when the favorite
loses surprisingly.
Factor graphs and
expectation propagation via
moment matching are used to compute the
message passing equations which in turn compute the skills for the players.
Player ranks are displayed as the conservative estimate of their skill,
. This is conservative, because the system is 99% sure that the player's skill is actually higher than what is displayed as their rank.
The system can be used with arbitrary scales, but Microsoft uses a scale from 0 to 50 for Xbox Live. Hence, players start with a rank of
. This means that a new player's defeat results in a large sigma loss, which partially or completely compensates their mu loss. This explains why people may gain ranks from losses.
Use in other projects
TrueSkill is patented,
and the name is trademarked,
so it is limited to Microsoft projects and commercial projects that obtain a license to use the algorithm.
See also
*
Software patents
A software patent is a patent on a piece of software, such as a computer program, library, user interface, or algorithm. The validity of these patents can be difficult to evaluate, as software is often at once a product of engineering, something ...
References
External links
Microsoft Research's TrueSkill homepageMicrosoft Research's TrueSkill paper
{{Microsoft Research
Tournament rating systems
-
Xbox network