The Condorcet Efficiency of Voting Rules with Mutually Coherent Voter Preferences : A Borda Compromise

The Condorcet Efficiency of a voting rule is defined as the conditional probability that the voting rule elects the Pairwise Majority Rule Winner (PMRW), given that a PMRW exists. Five simple voting rules are considered in this paper: Plurality Rule, Negative Plurality Rule, Borda Rule, Plurality Elimination Rule and Negative Plurality Elimination Rule. In order to study the impact that the presence of degrees of group mutual coherence in voting situations will have on the probability of selecting the PMRW for each of these rules, we develop representations for their Condorcet Efficiency as a function of the proximity of voters’ preferences on candidates to being perfectly singlepeaked, perfectly single-troughed or perfectly polarized. The results we obtain lead us to appeal for a Borda Compromise.