Axioms for defeat in democratic elections

We propose six axioms concerning when one candidate should defeat another in a democratic election involving two or more candidates. Five of the axioms are widely satisfied by known voting procedures. The sixth axiom is a weakening of Kenneth Arrow’s famous condition of the Independence of Irrelevant Alternatives (IIA). We call this weakening Coherent IIA. We prove that the five axioms plus Coherent IIA single out a method of determining defeats studied in our recent work: Split Cycle. In particular, Split Cycle provides the most resolute definition of defeat among any satisfying the six axioms for democratic defeat. In addition, we analyze how Split Cycle escapes Arrow’s impossibility theorem and related impossibility results.

Schrödinger’s Ballot: Quantum Information and the Violation of Arrow’s Impossibility Theorem

We study Arrow’s Impossibility Theorem in the quantum setting. Our work is based on the work of Bao and Halpern, in which it is proved that the quantum analogue of Arrow’s Impossibility Theorem is not valid. However, we feel unsatisfied about the proof presented in Bao and Halpern’s work. Moreover, the definition of Quantum Independence of Irrelevant Alternatives (QIIA) in Bao and Halpern’s work seems not appropriate to us. We give a better definition of QIIA, which properly captures the idea of the independence of irrelevant alternatives, and a detailed proof of the violation of Arrow’s Impossibility Theorem in the quantum setting with the modified definition.

Roberts’ weak welfarism theorem: a minor correction

Roberts’ “weak neutrality” or “weak welfarism” theorem concerns Sen social welfare functionals which are defined on an unrestricted domain of utility function profiles and satisfy independence of irrelevant alternatives, the Pareto condition, and a form of weak continuity. Roberts (Rev Econ Stud 47(2):421–439, 1980) claimed that the induced welfare ordering on social states has a one-way representation by a continuous, monotonic real-valued welfare function defined on the Euclidean space of interpersonal utility vectors—that is, an increase in this welfare function is sufficient, but may not be necessary, for social strict preference. A counter-example shows that weak continuity is insufficient; a minor strengthening to pairwise continuity is proposed instead and its sufficiency demonstrated.

The Order-Dependent Luce Model

I develop a simple axiomatic model that incorporates the order effect: the ordering of alternatives (e.g., ranking of universities, the location of products in a grocery store, the order of candidates on a ballot) affects choice frequencies. In my model, the probability of choosing an alternative is proportional to the utility of the alternative, similar to the Luce model. However, the utility of the alternative depends on the relative ordering of the alternative in the menu. I characterize this model by two weakenings of Luce’s axiom of independence of irrelevant alternatives. I discuss how to identify the ordering of alternatives from choice data when it is not observed. Finally, I apply my model to an optimal ordering problem and to experimental data on intertemporal choice. This paper was accepted by Manel Baucells, decision analysis.

Strategy-Proofness, Independence of Irrelevant Alternatives, and Majority Rule

We show that strategy-proofness, the Pareto principle, anonymity, neutrality, independence of irrelevant alternatives, and decisiveness uniquely characterize majority rule on any domain of preferences for which there exists a voting rule satisfying these axioms. In our formulation, strategy-proofness includes manipulations by coalitions. However, we demonstrate that the characterization still holds when coalitions are restricted to arbitrarily small size. We also show that when coalitions can manipulate outside the domain, there is an extension of majority rule that satisfies these axioms on any domain without Condorcet cycles. (JEL D72)

Set and revealed preference axioms for multi-valued choice

We consider choice correspondences that assign a subset to every choice set of alternatives, where the total set of alternatives is an arbitrary finite or infinite set. We focus on the relations between several extensions of the condition of independence of irrelevant alternatives on one hand, and conditions on the revealed preference relation on sets, notably the weak axiom of revealed preference, on the other hand. We also establish the connection between the condition of independence of irrelevant alternatives and so-called strong sets; the latter characterize a social choice correspondence satisfying independence of irrelevant alternatives.