Strategy-proof preference aggregation: Possibilities and characterizations

An aggregation rule maps each profile of individual strict preference orderings over a set of alternatives into a social ordering over that set. We call such a rule strategyproof if misreporting one’s preference never produces a different social ordering that is between the original ordering and one’s own preference. After describing two examples of manipulable rules, we study in some detail three classes of strategy-proof rules: (i) rules based on a monotonic alteration of the majority relation generated by the preference profile; (ii) rules improving upon a fixed status-quo; and (iii) rules generalizing the Condorcet-Kemeny aggregation method. Journal of Economic Literature Classification Number: D71. ∗ This research project was begun during Sprumont’s visit at the Indian Statistical Institute in New Delhi in 2010–2011. He is most grateful to the members of the ISI for their hospitality and thanks Arunava Sen for stimulating conversations. We thank the Fonds de Recherche sur la Société et la Culture of Québec and the Social Sciences and Humanities Research Council of Canada for financial support. The comments of an associate editor and two referees are gratefully acknowledged.