Multi-profile intergenerational social choice

In an infinite-horizon setting, Ferejohn and Page showed that any social welfare function satisfying Arrow’s axioms and stationarity must be a dictatorship of the first generation. Packel strengthened this result by proving that no collective choice rule generating complete social preferences can satisfy unlimited domain, weak Pareto and stationarity. We prove that this impossibility survives under a domain restriction and without completeness. We propose an alternative stationarity axiom and show that a social welfare function on a specific domain satisfies this modified version and some standard social choice axioms if and only if it is a chronological dictatorship.     

Coalitionally strategy-proof social choice correspondences and the Pareto rule

This paper studies coalitional strategy-proofness of social choice correspondences that map preference profiles into sets of alternatives. In particular, we focus on the Pareto rule, which associates the set of Pareto optimal alternatives with each preference profile, and examine whether or not there is a necessary connection between coalitional strategy-proofness and Pareto optimality. The definition of coalitional strategy-proofness is given on the basis of a max–min criterion. We show that the Pareto rule is coalitionally strategy-proof in this sense. Moreover, we prove that given an arbitrary social choice correspondence satisfying the coalitional strategy-proofness and nonimposition, all alternatives selected by the correspondence are Pareto optimal. These two results imply that the Pareto rule is the maximal correspondence in the class of coalitionally strategy-proof and nonimposed social choice correspondences.     

Partially efficient voting by committees

On the separable preference domain, voting by committees is the only class of voting rules that satisfy strategy-proofness and unanimity, and dictatorial rules are the only ones that are strategy-proof and Pareto efficient. To fill the gap, we define a sequence of efficiency conditions. We prove that for strategy-proof rules on the separable preference domain, the various notions of efficiency reduce to three: unanimity, partial efficiency, and Pareto efficiency. We also show that on the domain, strategy-proofness and partial efficiency characterize the class of voting rules represented as simple games which are independent of objects, proper and strong. We call such rules voting by stable committee.The author is deeply indebted to William Thomson for many helpful discussions on an earlier draft. The current version is greatly benefited from detailed comments of an anonymous referee. Thanks are also due to Jeffrey Banks, Salvador Barberà, Marcus Berliant, Ryo-ichi Nagahisa, Takehiko Yamato, and participants in a seminar at Rochester in 1992, the 1992 Midwest Conference at Michigan State, and the 1993 Summer Meeting of Econometric Society at Boston University for conversations and suggestions.     

On strategy-proofness and essentially single-valued cores: A converse result

In a general model of indivisible good allocation, S?nmez (1999) established that, whenever the core is nonempty for each preference profile, if an allocation rule is strategy-proof, individually rational and Pareto optimal, then the rule is a selection from the core correspondence, and the core correspondence must be essentially single-valued. This paper studies the converse claim of this result. I demonstrate that whenever the preference domain satisfies a certain condition of `richness', if the core correspondence is essentially single-valued, then any selection from the core correspondence is strategy-proof (even weakly coalition strategy-proof, in fact). In particular, on the domain of preferences in which each individual has strict preferences over his own assignments and there is no consumption externality, such an allocation rule is coalition strategy-proof. And on this domain, coalition strategy-proofness is equivalent to Maskin monotonicity, an important property in implementation theory. Received: 22 February 2000/Accepted: 22 January 2002 I am grateful to Ryo-ichi Nagahisa, Shinji Ohseto, Hiroshi Ono, Tomoichi Shinotsuka and Shigehiro Serizawa for valuable comments. And I am indebted to two anonymous referees for useful suggestions. Especially, I owe the present proof of Lemma 2 to one referee. I also thank Yukihiko Funaki, Atsushi Kajii, Mamoru Kaneko, Eiichi Miyagawa, Tatsuyoshi Saijo, Manimay Sengupta, Yves Sprumont, Yoshikatsu Tatamitani, Manabu Toda, Takashi Ui, Takehiko Yamato, Naoki Yoshihara and the participants of the seminars in Hokkaido University, Kansai University, ISER (Osaka University), Otaru University of Commerce and Tsukuba University. All errors are my own responsiblity.     

An alternative characterization of the uniform rule

We consider the problem of allocating some amount of a commodity among a group of agents with single-peaked preferences. We show that the uniform rule is the only rule satisfying equal treatment of equals, Pareto efficiency, and strategy-proofness. This characterization strengthens two interesting results due to Sprumont (1991). Our method of proof involves only elementary arguments.I wish to thank Professor William Thomson for his enormous efforts in supervision. I am grateful to Professor Marcus Berliant and Hideo Konishi for their useful remarks and especially to an anonymous referee for insightful comments. All remaining errors are my own responsibility.     

Gibbardian libertarian claims revisited

Two resolution schemes for the impossibility theorems on the Gibbard-Kelly claims of libertarian rights, which are rather contrasting with each other, are proposed and their implications discussed. The first scheme asserts that there exists a collective choice rule satisfying the Pareto principle and the Gibbard-Kelly libertarian claims if there exists at least one socially unconcerned individual. The second scheme asserts existence of an eligible collective choice rule if there exists at least one liberal individual.     

Social threshold aggregations

A problem of axiomatic construction of a social decision function is studied for the case when individual opinions of agents are given as m-graded preferences with arbitrary integer m ≥ 3. It is shown that the only rule satisfying the introduced axioms of Pairwise Compensation, Pareto Domination and Noncompensatory Threshold and Contraction is the threshold rule.     

Identification of domain restrictions over which acyclic, continuous-valued, and positive responsive social choice rules operate

We consider a social choice problem in various economic environments consisting of n individuals, 4≤n<+∞, each of which is supposed to have classical preferences. A social choice rule is a function associating with each profile of individual preferences a social preference that is assumed to be complete, continuous and acyclic over the alternatives set. The class of social choice rules we deal with is supposed to satisfy the two conditions; binary independence and positive responsiveness. A new domain restriction for the social choice rules is proposed and called the classical domain that is weaker than the free triple domain and holds for almost all economic environments such as economies with private and/or public goods. In this paper we explore what type of classical domain that admits at least one social choice rule satisfying the mentioned conditions to well operate over the domain. The results we obtained are very negative: For any classical domain admitting at least one social choice rule to well operate, the domain consists only of just one profile.     

A Note on the Separability Principle in Economies with Single-Peaked Preferences

We consider the problem of allocating an infinitely divisible commodity among a group of agents with single-peaked preferences. A rule that has played a central role in the analysis of the problem is the so-called uniform rule. Chun (2001) proves that the uniform rule is the only rule satisfying Pareto optimality, no-envy, separability, and Ω-continuity. We obtain an alternative characterization by using a weak replication-invariance condition, called duplication-invariance, instead of Ω-continuity. Furthermore, we prove that the equal division lower bound and separability imply no-envy. Using this result, we strengthen one of Chun’s (2001) characterizations of the uniform rule by showing that the uniform rule is the only rule satisfying Pareto optimality, the equal division lower bound, separability, and either Ω-continuity or duplication-invariance.     

Unequivocal majority and Maskin-monotonicity

The unequivocal majority of a social choice rule is a number of agents such that whenever at least this many agents agree on the top alternative, then this alternative (and only this) is chosen. The smaller the unequivocal majority is, the closer it is to the standard (and accepted) majority concept. The question is how small can the unequivocal majority be and still permit the Nash-implementability of the social choice rule; i.e., its Maskin-monotonicity. We show that the smallest unequivocal majority compatible with Maskin-monotonicity is n- ë \fracn-1m û{n-\left\lfloor \frac{n-1}{m} \right\rfloor} , where n ≥ 3 is the number of agents and m ≥ 3 is the number of alternatives. This value is equal to the minimal number required for a majority to ensure the non-existence of cycles in pairwise comparisons. Our result has a twofold implication: (1) there is no Condorcet consistent social choice rule satisfying Maskin-monotonicity and (2) a social choice rule satisfies k-Condorcet consistency and Maskin-monotonicity if and only if k 3 n- ë \fracn-1m û{k\geq n-\left\lfloor \frac{n-1}{m}\right\rfloor}.     

Some implications of an intensity measure of envy

This article proposes a cardinal or an intensity measure of interpersonal envy by directly measuring the distance between the envied person's consumption bundle and the envious person's equilibrium indifference curve. The individual's intensity of envy is aggregated to form a social envy index, which in turn is combined with the Pareto criterion to form a social choice rule. This social choice rule generates a non-empty choice set with the fair set (envy-free and Pareto efficient social states) as a proper subset of the choice set. The intensity measure of envy is then applied to the Rawlsian problem of the worst-off person. It turns out that the person with the greatest envy need not be the poorest person. Finally, it is shown that if individuals have homothetic and identical preferences the measure of envy collapses into a measure of income inequality. This measure of income inequality satisfies soem appealing axioms.I am grateful to William Vickrey and Duncan Foley for orginally encouraging the idea of intensity of envy. This version has benefited greatly from suggestions and criticisms made by F. William McElroy     

Public information and social choice

We examine the value of public information when a society uses a social choice rule to decide among a set of outcomes. We require that a social choice function satisfies unrestricted domain, non-decisiveness and the Pareto principle. We show that there exist payoff structures for every social choice function, such that an arbitrary subset of voters is worse off by public information. We apply the proposition to collective information acquisition and to irreversible investments. Received: 2 June 1997/Accepted: 30 September 1998     

Nondictatorially independent pairs

Suppose that social welfare function f satisfies the Pareto condition and has complete and transitive values. On a domain satisfying the free quadruple property, if the outcome set X has m< outcomes, then the set of pairs of distinct alternatives on which f satisfies both independence and nondictatorship contains at most the fraction 2/m of all pairs. On a domain satisfying the free six-tuple property, if X is a subset of Euclidean space then the set of pairs on which f satisfies both independence and nondictatorship has Lebesgue measure zero.Campbell's research was financed by the National Science Foundation, grant SES 9209039.     

Collective choice rules and collective rationality: a unified method of characterizations

The purpose of this paper is to investigate the relationship between collective rationality and permissible collective choice rules using a unified approach inspired by Bossert and Suzumura (J Econ Theory 138:311–320, 2008). We consider collective choice rules satisfying four axioms: unrestricted domain, strong Pareto, anonymity, and neutrality. A number of new classes of collective choice rules as well as the Pareto and Pareto extension rules are characterized under various concepts of collective rationality: acyclicity, transitivity, quasi-transitivity, semi-transitivity, and the interval order property. Further, new concepts of collective rationality, K-term acyclicity and K-term consistency, are proposed and the corresponding characterizations are provided.     

Veto in fixed agenda social choice correspondences

In this paper we analyze the relationship between social decision functions (SDF) and fixed agenda social choice correspondences (fixed agenda SCC), satisfying some rationality conditions (such as Pareto, Independence, Monotonicity, Neutrality or Anonimity), with the aim of translating known results on the existence of individuals with veto power into the fixed agenda framework (e.g., Blair and Pollak [2], Blau and Deb [3], …). In order to do this, a new independence condition (which we call Pseudo-Independence), as well as a notion of veto power, are introduced in the context of fixed agenda SCC. The conclusion is that, by fixing the agenda, under Independence and Pareto assumptions, the existence of individuals with veto power cannot be avoided. Received: 6 November 1995 / Accepted: 9 September 1997     

Resource-monotonic solutions to the problem of fair division when preferences are single-peaked

We consider the problem of fairly allocating an infinitely divisible commodity among a group of agents with single-peaked preferences. We search for solutions satisfying resource-monotonicity, the requirement that all agents be affected in the same direction when the amount to divide changes. Although there are resource-monotonic selections from the Pareto solution, there are none satisfying the distributional requirements of no-envy or individual rationality from equal division. We then consider the weakening of resource-monotonicity obtained by allowing only changes in the amount to divide that do not reverse the direction of the inequality between the amount to divide and the sum of the preferred amounts. We show that there is essentially a unique selection from the solution that associates with each economy its set of envy-free and efficient allocations satisfying this property of one-sided resource-monotonicity: it is the uniform rule, a solution that has played a central role in previous analyses of the problem.     

Equivalence of Nash implementability and robust implementability with incomplete information

This paper is concerned with the design of robust mechanisms which are applicable to a wide class of possible information structures of agents. We examine a society consisting of several groups such that (i) there are at least three agents in each group; and (ii) each agent knows the preferences of the agents in his group but has incomplete information about the preferences of the agents outside his group. We show that for a large class of information structures, a social choice set (SCS) is implementable for each possible information structure if and only if it is Nash implementable. In other words, the class of robustly implementable SCS's is identical to the class of implementable SCS's in the complete information setting.This paper is a substantially revised version of a chapter of my dissertation submitted to the University of Rochester (Yamato [25]). I thank Professor William Thomson for his invaluable advice and suggestions. Detailed comments and suggestions of an anonymous referee were very helpful for further revision of the paper. I also acknowledge comments from Professors Randall Calvert, Luis Corchon, Glenn MacDonald, Eric Maskin, Lionel McKenzie, Ryo-Ichi Nagahisa, Koji Okuguchi, Ignacio Ortuño-Ortin, Tatsuyoshi Saijo, Ken-Ichi Shimomura, Tomas Sjöström, Yoshikatsu Tatamitani, and seminar participants at Harvard University, the 1992 Meeting of Kobe Summer Seminar in Economics of Organization and Game Theory, Tokyo Metropolitan University, and Toyama University. This work was supported in part by the Ministry of Education in Japan, the Nomura Foundation for the Social Sciences, and the Tokyo Center for Economic Research.     

Balanced consistency and balanced cost reduction for sequencing problems

We investigate the implications of balanced consistency and balanced cost reduction in the context of sequencing problems. Balanced consistency requires that the effect on the payoff from the departure of one agent to another agent should be equal between any two agents. On the other hand, balanced cost reduction requires that if one agent leaves a problem, then the total payoffs of the remaining agents should be affected by the amount previously assigned to the leaving agent. We show that the minimal transfer rule is the only rule satisfying efficiency and Pareto indifference together with either one of our two main axioms, balanced consistency and balanced cost reduction.     

Social compromise and social metrics

In the context of constitutional design, a committee of citizens' representatives proposes (social choice) axioms. The outcome should not necessarily be the aggregation rule, or rules, satisfying each of the axioms. Alternative procedures are recommended for aggregating a set of axioms into a single summary axiom. The summary axiom generates a single social decision function when a social metric is applied.     

Nonmanipulable decision mechanisms for economic environments

In the social choice literature studying the problem of designing institutions for collective decision making, it is customary to (implicitly) assume that each dimension of the social outcome is of public interest (i.e., that each individual's welfare depends on every dimension of the outcome). Thus, the scope of the conclusions obtained is very limited. Here social decision problems with and without that public character are considered and it is shown that the same negative results arise in most cases; namely, that only dictatorial mechanisms are immune to the participants' manipulations. These results are obtained without requiring that the mechanisms produce Pareto optimal outcomes (they must simply be minimally responsive to the participants' preferences), which deepens their pessimistic character.I am deeply grateful to my advisor, Mark Walker, for his continuous guidance and encouragement. I wish also to thank Salvador Barberà, John Weymark, and two anonymous referees for helpful comments.