Social utility efficiency


Social utility efficiency is a measurement of the utilitarian performance of voting methods—how likely they are to elect the candidate who best represents the voters' preferences.
It is also known as Voter Satisfaction Index or Voter Satisfaction Efficiency. Bayesian Regret measures the same property, but inverted and non-normalized.
Social utility efficiency is defined as the ratio between the social utility of the candidate who is elected by a given voting method and that of the candidate who maximizes social utility, where is the expected value over many iterations:
A voting method with 100% efficiency would always pick the candidate that maximizes voter utility. A method that chooses a winner randomly would have efficiency of 0%, and a method that did worse than a random pick would have less than 0% efficiency.
SUE is not only affected by the voting method, but is a function of the number of voters, number of candidates, and of any strategies used by the voters.
The concept was originally introduced as a system's "effectiveness" by Weber in 1977, using a random society model, but it has since been extended to the more realistic spatial model of voting and a hierarchical clusters model.