Condorcet efficiency is a measurement of the performance of

voting methods Voting is a method by which a group, such as a meeting or an electorate, can engage for the purpose of making a collective decision or expressing an opinion usually following discussions, debates or election campaigns. Democracies elect holde ...

. It is defined as the percentage of elections for which the

Condorcet winner An electoral system satisfies the Condorcet winner criterion () if it always chooses the Condorcet winner when one exists. The candidate who wins a majority of the vote in every head-to-head election against each of the other candidatesthat is, a ...

(the candidate who is preferred over all others in head-to-head races) is elected, provided there is one. A voting method with 100% efficiency would always pick the Condorcet winner, when one exists, and a method that never chose the Condorcet winner would have 0% efficiency. The outcome of a referendum on policy can be efficient if the conditions of the

efficient voter rule In the study of voter behavior, the efficient voter rule speaks to the desirability of voter-driven outcomes. It applies to situations involving negative externalities such as pollution and crime, and positive externalities such as education. Relate ...

are met. Efficiency 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. It was initially developed in 1984 by

Samuel Merrill III Samuel Merrill III (born 1939) is an American mathematician and political scientist best known for his work on alternative voting systems, voter behavior, party competition, and arbitration. Merrill was raised in Bogalusa, Louisiana. He received h ...

, along with

Social utility efficiency Social utility efficiency (SUE) 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 utilitarian efficiency, voter satisfac ...

. A related, generalized measure is Smith efficiency, which measures how often a voting method elects a candidate in the

Smith set In voting systems, the Smith set, named after John H. Smith, but also known as the top cycle, or as Generalized Top-Choice Assumption (GETCHA), is the smallest non-empty set of candidates in a particular election such that each member defeats ever ...

. Except in elections where the Smith set includes all candidates, Smith efficiency is a measure that can be used to differentiate between voting methods in all elections, because unlike the CW, the Smith set always exists. A 100%

Smith-efficient In voting systems, the Smith set, named after John H. Smith, but also known as the top cycle, or as Generalized Top-Choice Assumption (GETCHA), is the smallest non-empty set of candidates in a particular election such that each member defeats ever ...

method is guaranteed to be 100% Condorcet-efficient, and likewise with 0%.

References

{{election-stub Voting theory Electoral systems

See also

References