TrueSkill is a skill-based ranking system developed by
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washi ...
for use with video game matchmaking on
Xbox Live
The Xbox network, formerly and still sometimes branded as Xbox Live, is an online multiplayer gaming and digital media delivery service created and operated by Microsoft. It was first made available to the Xbox system on November 15, 2002. A ...
. 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. It is named after its creator Arpad Elo, a Hungarian-American physics professor.
The Elo system was invented as an improved c ...
, which was initially designed for
chess
Chess is a board game for two players, called White and Black, each controlling an army of chess pieces in their color, with the objective to checkmate the opponent's king. It is sometimes called international chess or Western chess to dist ...
, TrueSkill is designed to support games with more than two players.
In 2018, Microsoft published details about an extended version of TrueSkill, named TrueSkill2.
Calculation
A player's skill is represented as a
normal distribution
In 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 e^
The parameter \mu ...
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 graph
A factor graph is a bipartite graph representing the factorization of a function. In probability theory and its applications, factor graphs are used to represent factorization of a probability distribution function, enabling efficient computatio ...
s and
expectation propagation
Expectation propagation (EP) is a technique in Bayesian machine learning.
EP finds approximations to a probability distribution. It uses an iterative approach that uses the factorization structure of the target distribution. It differs from oth ...
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, libraries, user interface, or algorithm.
Background
A patent is a set of exclusionary rights granted by a state to a patent holder for a limited period of time, u ...
References
External links
Microsoft Research's TrueSkill homepageMicrosoft Research's TrueSkill paper
{{Microsoft Research
Rating systems
Games for Windows
Xbox network