Neutrality, Pairwise Justifiability and Serial Dictatorships

• Authors: Pietro Salmanso, Bernardo Moreno and Dolors Berga.
• BSE Working Paper: 1508 | September 25
• Keywords: collective choice correspondences , neutrality , serial dictators
• JEL codes: D70, D71, D78

We consider a society composed of a finite set of agents with preferences over a finite set of alternatives. We focus on collective choice correspondences which are rules assigning to each pair formed by agents’ preferences and a subset of alternatives (an agenda), a chosen subset of the agenda. Our analysis centers on three properties: neutrality, strong pairwise justifiability, and strong decisiveness. Neutrality requires that no alternative is intrinsically favored over another. Strong pairwise justifiability demands that if an alternative x is selected in one situation but not in another, there must exist some other alternative z , present in both agendas, whose relative ranking with respect to x has improved for at least one agent. Strong decisiveness is a property that can be viewed as a particular type of resoluteness. Our main result establishes that serial dictatorships are the only collective choice correspondences defined on the universal domain and across all agendas satisfying neutrality, strong pairwise justifiability, and strong decisiveness.