Comment on the Kannai-Peleg impossibility theorem for extending orders

Recent work by Y. Kannai and B. Peleg shows that two appealing axioms for extending a linear order on a set of six or more elements to a weak order on the family of non-empty subsets of that set are mutually incompatible. This comment shows that a modest restriction of their monotonicity axiom is compatible for extension with a generalization of their other axiom provided that the linear order on the basic set is a well ordering.     

A unifying impossibility theorem

This paper identifies and illuminates a common impossibility principle underlying a number of impossibility theorems in social choice. We consider social choice correspondences assigning a choice set to each non-empty subset of social alternatives. Three simple axioms are imposed as follows: unanimity, independence of preferences over infeasible alternatives, and choice consistency with respect to choices out of all possible alternatives. With more than three social alternatives and the universal preference domain, any social choice correspondence that satisfies our axioms is serially dictatorial. A number of known impossibility theorems—including Arrow’s Impossibility Theorem, the Muller–Satterthwaite Theorem, and the impossibility theorem under strategic candidacy—follow as corollaries.     

A general impossibility result on strategy-proof social choice hyperfunctions

A social choice hyperfunction picks a non-empty set of alternatives at each admissible preference profile over sets of alternatives. We analyze the manipulability of social choice hyperfunctions. We identify a domain D^λ of lexicographic orderings which exhibits an impossibility of the Gibbard–Satterthwaite type. Moreover, this impossibility is inherited by all well-known superdomains of D^λ. As most of the standard extension axioms induce superdomains of D^λ while social choice correspondences are particular social choice hyperfunctions, we are able to generalize many impossibility results in the literature.     

Social orderings for the assignment of indivisible objects

In the assignment problem of indivisible objects with money, we study social ordering functions which satisfy the requirement that social orderings should be independent of changes in preferences over infeasible bundles. We combine this axiom with efficiency, consistency and equity axioms. Our result is that the only social ordering function satisfying those axioms is the leximin function in money utility.     

An extension of Fishburn's theorem on extending orders

P. C. Fishburn [J. Econom. Theory31 (1983), 000-000] has shown that one can extend any well ordering of a set to a linear ordering of the set of all non-empty subsets of that set, while satisfying two axioms denoted (GP¹) and (M¹). By applying the compactness theorem of logic, this note shows that the well ordering assumption can be waived. Definability and well ordering properties of the extension are also discussed and shown to depend on the class of basic orderings considered.     

Feasible elimination procedures in social choice: An axiomatic characterization

Feasible elimination procedures (Peleg, 1978) play a central role in constructing social choice functions which have the following property: in the associated game form, for any preference profile there exists a strong Nash equilibrium resulting in the sincere outcome. In this paper we provide an axiomatic characterization of the social choice correspondences resulting from applying feasible elimination procedures. The axioms are anonymity, Maskin monotonicity, and independent blocking. We also show that these axioms are logically independent.     

A uniqueness result for extending orders; with application to collective choice as inconsistency resolution

Two axioms about extending a weak ordering of a set Ω to its power set 2^Ω uniquely determine a lexicographic weak ordering of 2^Ω. The solution is applied to collective choice to resolve majority cycle inconsistencies, and also contrasted with Condorcet.     

The veil of public ignorance

A theory of cooperative choice under incomplete information is developed in which agents possess private information at the time of contracting and have agreed on a utilitarian “standard of evaluation” governing choices under complete information. The task is to extend this standard to situations of incomplete information. Our first main result generalizes Harsanyi's (J. Polit. Econ. 63 (1955) 309) classical result to situations of incomplete information, assuming that group preferences satisfy Bayesian Coherence and Interim Pareto Dominance. These axioms are mutually compatible if and only if a common prior exists. We argue that this result partly resolves the impossibility of Bayesian preference aggregation under complete information.     

The measurement of income mobility: A partial ordering approach

Summary. Given a set of longitudinal data pertaining to two populations, a question of interest is the following: Which population has experienced a greater extent of income mobility? The aim of the present paper is to develop a systematic way of answering this question. We first put forth four axioms for income movement-mobility indices, and show that a familiar class of measures is characterized by these axioms. An unambiguous (partial) ordering is then defined as the intersection of the (complete) orderings induced by the mobility measures which belong to the characterized class; a transformation of income distributions is “more mobile” than another if, and only if, the former is ranked higher than the latter for all mobility measures which satisfy our axioms. Unfortunately, our mobility ordering depends on a parameter, and therefore, it is not readily apparent how one can apply it to panel data directly. In the second part of the paper, therefore, we derive several sets of parameter-free necessary and sufficient conditions which allow one to use the proposed mobility ordering in making unambiguous income mobility comparisons in practice. Received: July 12, 1995; revised version: May 13, 1997     

Attitude toward imprecise information

This paper presents an axiomatic model of decision making under uncertainty which incorporates objective but imprecise information. Information is assumed to take the form of a probability–possibility set, that is, a set P of probability measures on the state space. The decision maker is told that the true probability law lies in P and is assumed to rank pairs of the form (P,f) where f is an act mapping states into outcomes. The key representation result delivers maxmin expected utility (MEU) where the min operator ranges over a set of probability priors—just as in the MEU representation result of Gilboa and Schmeidler [Maxmin expected utility with a non-unique prior, J. Math. Econ. 18 (1989) 141–153]. However, unlike the MEU representation, the representation here also delivers a mapping, , which links the probability–possibility set, describing the available information, to the set of revealed priors. The mapping is shown to represent the decision maker's attitude to imprecise information: under our axioms, the set of representation priors is constituted as a selection from the probability–possibility set. This allows both expected utility when the selected set is a singleton and extreme pessimism when the selected set is the same as the probability–possibility set, i.e., is the identity mapping. We define a notion of comparative imprecision aversion and show it is characterized by inclusion of the sets of revealed probability distributions, irrespective of the utility functions that capture risk attitude. We also identify an explicit attitude toward imprecision that underlies usual hedging axioms. Finally, we characterize, under extra axioms, a more specific functional form, in which the set of selected probability distributions is obtained by (i) solving for the “mean value” of the probability–possibility set, and (ii) shrinking the probability–possibility set toward the mean value to a degree determined by preferences.     

Polarization Orderings and New Classes of Polarization Indices

This paper explores equivalent formulations of the polarization ordering first proposed by Foster and Wolfson. Motivated by the class of polarization indices proposed by Foster and Wolfson, we have developed a class of generalized Foster-Wolfson indices. In addition, a new class of polarization indices satisfying a set of desirable axioms is also derived.     

An axiomatic characterization of the Theil inequality ordering

We axiomatically characterize the Theil ordering of income inequality. In addition to the uncontroversial axioms of anonymity, homogeneity, replication invariance, strong directedness, and a standard continuity property, we appeal to both an independence and a decomposability axioms. These two axioms are ordinal implications of Theil decomposability, the central axiom in previous characterizations of the Theil index. To the best of our knowledge, the present is the first fully ordinal characterization of this index.     

Two characterizations of the uniform rule for division problems with single-peaked preferences

Summary The uniform rule is considered to be the most important rule for the problem of allocating an amount of a perfectly divisible good between agents who have single-peaked preferences. The uniform rule was studied extensively in the literature and several characterizations were provided. The aim of this paper is to provide two different formulations and corresponding axiomatizations of the uniform rule. These formulations resemble the Nash and the lexicographic egalitarian bargaining solutions; the corresponding axiomatizations are based on axioms of independence of irrelevant alternatives and restricted monotonicity.The authors are grateful to Jeffrey Banks, Steve Ching, Vincent Feltkamp, Bezalel Peleg, Sang-Young Sonn, William Thomson and an anonymous referee for helpful comments.     

Temptation-Driven Preferences

"My own behaviour baffles me. For I find myself not doing what I really want to do but doing what I really loathe." Saint Paul
What behaviour can be explained using the hypothesis that the agent faces temptation but is otherwise a "standard rational agent"? In earlier work, Gul and Pesendorfer (2001) use a set betweenness axiom to restrict the set of preferences considered by Dekel, Lipman and Rustichini (2001) to those explainable via temptation. We argue that set betweenness rules out plausible and interesting forms of temptation including some which may be important in applications. We propose a pair of alternative axioms called DFC, desire for commitment , and AIC, approximate improvements are chosen . DFC characterizes temptation as situations in which given any set of alternatives, the agent prefers committing herself to some particular item from the set rather than leaving herself the flexibility of choosing later. AIC is based on the idea that if adding an option to a menu improves the menu, it is because that option is chosen under some circumstances. From this interpretation, the axiom concludes that if an improvement is worse (as a commitment) than some commitment from the menu, then the best commitment from the improved menu is strictly preferred to facing that menu. We show that these axioms characterize a natural generalization of the Gul–Pesendorfer representation.     

Ranking opportunity sets in a simple intertemporal framework

We extend the problem of ranking subsets (opportunity sets) of a set of alternatives to an intertemporal setting, whereby the agent makes a sequence of choice decisions over time. In particular, we show in a simple two-period model that an agent who satisfies five plausible axioms ranks opportunity sets in a lexicographic fashion. That is, the agent ranks opportunity sets based solely on the relative desirability of their first-period alternatives, and only if the first-period alternatives are thought equally desirable does the agent consider the second-period alternatives. We discuss this strong time-discounting result and the role of the axioms, and also show that the popular “independence” axioms employed in the existing “static” literature are inconsistent with some reasonable axioms regarding intertemporal choice.      

Biodiversity measures based on species-level dissimilarities: A methodology for assessment

Biodiversity is widely recognized as a valuable natural asset to conserve. Yet biodiversity is often reported to be declining worldwide. Biodiversity measures can help evaluating it and conserving it, but need to be clearly defined and assessed. In this paper, I review several biodiversity measures and develop a new one, all based on a matrix of species-level dissimilarity data. The data can be used in its raw form, regardless of its origin (e.g. studies of morphological traits, DNA hybridization experiments…) or of any graphical representation. Then, I propose a two-step assessment of the measures. First, I assess them in terms of their deviation from a strict additive law determining the contribution of each species to the diversity of the set in an ideal setting. This setting refers to a case where the data exactly determines the hierarchical ordering of the species. Second, I assess the measures based on their compliance with a list of axioms. These axioms reflect basic mathematical properties regarded as desirable for diversity measures, such as their monotonicity in species and dissimilarities. Finally, I show the importance of applying the new quantitative assessment and the axiomatic approach together when selecting a dissimilarity-based diversity measure.     

Preference for flexibility in infinite horizon problems

Summary. We consider the extension of the classical problem of preference for flexibility to many periods. Preferences are defined over sets of infinite paths of choices. The main result provides a set of axioms on preferences that yield an additive representation over a subjective state space. This space is the set of preferences over choice today and feasible set tomorrow. The main new axiom, stochastic dominance, is a stronger form of the assumption of monotonicity. Received: September 11 2000; revised version: December 18, 2001     

Implementation in undominated strategies by bounded mechanisms: Some results on compromise alternatives

We consider an impossibility result in Börgers (1991), which says in a restricted environment with two players or three alternatives it is impossible to implement a social choice correspondence that is efficient, enforces compromises at a profile and is implementable in undominated strategies by a bounded mechanism. We extend and refine this result in many ways- we generalize the impossibility result for any number of players and alternatives when the compromises are enforced at a near-unanimous preference profile. We further show that the impossibility result in Börgers (1991) holds good if we replace efficiency of SCCs by neutrality. Also the impossibility result holds good for two agents and any number of alternatives when the SCC is unanimous and minimal. Interestingly, we get a possibility result when we relax the assumption of minimality.     

Revisiting Savage in a conditional world

Summary. I present an axiomatization of subjective expected utility and Bayesian updating in a conditional decision problem. This result improves our understanding of the Bayesian standard from two perspectives: 1) it uses a set of axioms which are weak and intuitive; 2) it provides a formal proof to results on the relation between dynamic consistency, expected utility and Bayesian updating which have never been explicitly proved in a fully subjective framework. Received: December 1, 2000; revised version: February 26, 2001     

Median-based extensions of an ordering over a set to the power set: An axiomatic characterization

In this paper we consider the problem of inducing an ordering over the set of all non-empty subsets of a finite set X of alternatives, given an ordering R over X. Assuming R to be antisymmetric and X to have at least six elements, we provide a set of independent, necessary, and sufficient conditions for the induced ordering to be “median-based” (so that every non-empty subset of X is “indifferent” to its own median set defined in terms of R).