Condorcet efficiency: A preference for indifference

The Condorcet winner in an election is the candidate who would be able to defeat all other candidates in a series of pairwise elections. The Condorcet efficiency of a voting procedure is the conditional probability that it will elect the Condorcet winner, given that a Condorcet winner exists. The st...

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Bibliographic Details
Published inSocial choice and welfare Vol. 18; no. 1; pp. 193 - 205
Main Authors Gehrlein, William V., Valognes, Fabrice
Format Journal Article
LanguageEnglish
Published Heidelberg Springer Science + Business Media 01.01.2001
Springer Nature B.V
Springer Verlag
Subjects
Ambivalence
Candidates
Conditional probabilities
Decision Making
Decision Models
Economic models
Economics and Finance
Efficiency
Elections
Electorate
Humanities and Social Sciences
Paradoxes
Plurality voting
Political candidates
Preferences
Probability
Rational Choice
Social services
Studies
Voter preferences
Voters
Voting Behavior
Voting paradox
Zero
Conditional Probability
Condorcet Winner
Borda Rule
Voter Preference
Vote Procedure
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Summary:The Condorcet winner in an election is the candidate who would be able to defeat all other candidates in a series of pairwise elections. The Condorcet efficiency of a voting procedure is the conditional probability that it will elect the Condorcet winner, given that a Condorcet winner exists. The study considers the Condorcet efficiency of weighted scoring rules (WSR's) on three candidates for large electorates when voter indifference between candidates is allowed. It is shown that increasing the proportion of voters who have partial indifference will increase the probability that a Condorcet winner exists, and will also increase the Condorcet efficiency of all WSR's. The same observation is observed when the proportion of voters with complete preferences on candidates is reduced. Borda Rule is shown to be the WSR with maximum Condorcet efficiency over a broad range of assumptions related to voter preferences. The result of forcing voters to completely rank all candidates, by randomly breaking ties on candidates that are viewed as indifferent, leads to a reduction in the probability that a Condorcet winner exists and to a reduction in the Condorcet efficiency of all WSR's.
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ISSN:0176-1714
1432-217X
DOI:10.1007/s003550000071