Voting Rules,Manipulability and Social Homogeneity

To what extent are some voting rules more vulnerable tostrategic manipulation than others? In order to answer thisquestion, representations are developed for the coalitionalmanipulability of eight voting rules under various assumptionsconcerning the likelihood that given voters' preferenceprofiles are observed on three alternatives. Of particularinterest is the impact that social homogeneity (defined as thetendency of voters' preference to be similar) has on themanipulability of voting rules. The results we obtain showthat the hierarchy of the voting rules that results from ourcomputations can crucially depend on the degree of socialhomogeneity. However, it turns out that, whatever the degreeof homogeneity, the Hare method (or two-stage plurality)minimizes susceptibility to strategic manipulation bycoalitions of voters in three-candidate elections.

     

On Some Limitations of the Median Voting Rule

Median Voting Rule (MVR) has been proposed as a voting rule,based on the argument that MVR will be less manipulable thanBorda Rule. We find that plurality rule has only a slightlygreater probability of manipulability than MVR, and thatCopeland Rule has a smaller probability of manipulability thanMVR. In addition Borda Rule, plurality rule and Copeland Ruleall have both a greater probability of producing a decisiveresult and a greater strict Condorcet efficiency than MVR.Based on all characteristics, MVR does not seem to be viablereplacement for either plurality rule or for Copeland Rule.