Strategy-proof allocation when preferences are single-plateaued

Abstract. We consider private good economies with single-plateaued preferences. A solution selects for each preference profile a non-empty set of allocations. An agent strictly prefers a set of allocations to another set of allocations if and only if he strictly prefers any allocation in the first set to any in the second set according to his single-plateaued preference relation. We characterize the class of sequential-allotment solutions by essentially single-valuedness, Pareto-indifference, and coalitional stragety-proofness. These solutions are the Pareto-indifferent extensions of the solutions studied by Barberà et al. 1997. Received: 9 May 2000 / Accepted: 1 May 2001     

Condorcet efficiency of positional voting rules with single-peaked preferences

Consider a three-alternative election with n voters and assume that preferences are single-peaked. LetC(λ,n) be the Condorcet efficiency of the rule that assigns 1,λ and 0 points (respectively) to each first, second and third place vote. An exact representation is obtained forC(λ,∞). This relation shows that Borda rule (λ=1/2) is not the most efficient rule. In addition to this result, exact closed form relations are provided forC(0,n),C(1/2,n) andC(1,n). All these relations are obtained by assuming that every admissible configuration of preferences is equally likely to occur. This research was supported in part by the Swedish Insitute     

Are serial Condorcet rules strategy-proof?

Abstract. This paper explores the extent to which majority rule is invulnerable to manipulation by individuals and coalitions, even when majority rule is used to select more than one alternative. The resulting rule may or may not be strategy-proof, depending on the size of the coalitions that can form, and on the nature of the individual preferences over sets of alternatives. No individual can manipulate with respect to a wide family of preferences over sets. The only restriction on the domain of true and revealed individual preferences is that the selection rule is always well defined. Received: 1 November 1999 / Accepted: 7 May 2001 We thank two anonymous referees for suggestions that have significantly improved the paper. We are also grateful to l'Université de Caen for sponsoring a Workshop on Social Choice Theory, where a first draft of this paper was presented in May, 1999, and to the workshop participants for helpful observations. Work on the final version of the paper was done while one of the authors was a guest of the Project on Intergenerational Equity supported by the Ministry of Education, Science, and Technology of Japan. We are grateful to the Ministry and to the project leader, Professor Kotaro Suzumura, for their support.     

May’s theorem in an infinite setting

We generalize May’s theorem to an infinite setting, preserving the elementary character of the original theorem. We define voting scenarios and generalized voting scenarios, and prove appropriate versions of May’s theorem. The case of generalized voting scenarios specialized to a countably infinite set of voters and the collections of all coalitions that have asymptotic density, shows that majority rule is the only aggregation rule that satisfies neutrality, irrelevance of null coalitions, anonymity, and positive responsiveness.     

Implementation and information in teams

A risk-neutral principal hires risk-averse agents to work in a team production process. Each agent can observe the actions taken by some subset of the other agents, and (perhaps) the realization of a random variable which is correlated with output. The principal cannot observe actions or the random variable. However, the agents can communicate with the principal, and final output is verifiable. We characterize the information structures that make it possible for the principal to implement his first best. In general it will be desirable to restrict the information available to the agents. If the first best can be implemented, then it can be implemented by a very simple mechanism, in which each agent forecasts the team output, but sends no other message.     

Implementation by demand mechanisms

This paper introduces a class of implementation mechanisms for exchange economies, calleddemand mechanisms. Each agent “demands” a consumption bundle, and equilibria are situations where each agent receives the bundle he asked for. A simple necessary and sufficient condition for implementation by a demand mechanism is derived.     

A topological approach to Wilson’s impossibility theorem

We will present a topological approach to Wilson’s impossibility theorem [Wilson, R.B., 1972. Social choice theory without the Pareto principle. Journal of Economic Theory 5, 478–486] that there exists no non-null binary social choice rule which satisfies transitivity, independence of irrelevant alternatives, non-imposition and has no dictator nor inverse dictator. Our research is in line with the studies of topological approaches to discrete social choice problems initiated by [Baryshnikov, Y., 1993. Unifying impossibility theorems: a topological approach. Advances in Applied Mathematics 14, 404–415]. This paper extends the result about the Arrow impossibility theorem shown in [Tanaka, Y., 2006. A topological approach to the Arrow impossibility theorem when individual preferences are weak orders. Applied Mathematics and Computation 174, 961–981] to Wilson’s theorem.     

Generalized time-invariant overtaking

We present a new version of the overtaking criterion, which we call generalized time-invariant overtaking. The generalized time-invariant overtaking criterion (on the space of infinite utility streams) is defined by extending proliferating sequences of complete and transitive binary relations defined on finite dimensional spaces. The paper presents a general approach that can be specialized to at least two, extensively researched examples, the utilitarian and the leximin orderings on a finite dimensional Euclidean space.     

A characterization and an impossibility of finite length anonymity for infinite generations

In the context of ranking infinite utility streams, the impartiality axiom of finite length anonymity requires the equal ranking of any two utility streams that are equal up to a finite length permutation ( Fleurbaey and Michel, 2003). We first characterize any finite length permutation as a composition of a fixed step permutation and an “almost” fixed step permutation. We then show that if a binary relation satisfies finite length anonymity, then it violates all the distributional axioms that are based on a segment-wise comparison. Examples of those axioms include the weak Pareto principle and the weak Pigou-Dalton principle.     

Strategy-proofness in many-to-one matching problems

We search forstrategy-proof solutions in the context of (many-to-one) matching problems (Gale and Shapley, 1962). In this model, whenever the firms can hire as many workers as they want (the capacities are unlimited) the stable set is a singleton. There exists aPareto efficient, individually rational, andstrategy-proof matching rule if and only if the capacities are unlimited. Furthermore, whenever the capacities unlimited, the matching rule which selects the unique stable matching is the only matching rule that isPareto efficient, individually rational, andstrategy-proof.     

Frequency based analysis of collective aggregation rules

A new property for collective aggregation rules called positive discrimination is introduced. This property is satisfied by many anonymous and neutral collective aggregation rules. We discuss unimodal profiles (or distributions) for which this property on its own determines the outcome as the mode of a unimodal distribution. We investigate relaxations of this unimodal distribution condition and show that the Condorcet consistent rules as well as the Borda rule and the plurality rule have the mode as the outcome at such profiles. Further, we show, by an example, how the addition of unimodal profiles and the property of positive discrimination can help to determine an outcome in the case of a large number of voters.     

Reduction-consistency in collective choice problems

We consider the problem of choosing a subset of a feasible set over which each agent has a strict preference. We propose an invariance property, reduction-consistency, of choice rules and study its implications. The property is a natural expression for the problems of a general principle of consistency having been studied extensively in resource allocation problems. We show that no scoring rule satisfies reduction-consistency, and base a characterization of the top rule on the property. We also investigate the minimal extension of a rule needed to recover reduction-consistency, and identify the minimal extensions of several rules including the Borda and plurality rules.     

Exchange-proofness or divorce-proofness? Stability in one-sided matching markets

Two stability concepts for one-sided matching markets are analyzed: Gale-Shapley stability and ξ-stability. The first one applies best to markets where no status quo allocation is considered, whereas the second one is a solution to be used when property rights are allowed. A common problem of existence is shared by both solution concepts. Hence, we study economic environments where this problem does not exist, and present a family of agents’ preferences for which existence is guaranteed for both Gale-Shapley stable and ξ-stable outcomes. This work was finished while the author was visiting Duke University, whose hospitality is gratefully acknowledged. Swveral discussions with Salvador Barberà, Hervé Moulin and Marilda Sotomayor and some advice by an anonymous referee were specially useful. This work is partially supported by Grants PB 92-0590 and PB 93-0938 from the DGICYT, the Spanish Ministery of Educación Ciencia, and the Institut Valencià d’Investigacions Econòmiques.     

Implementation of social optimum in oligopoly

This paper presents a decentralized mechanism implementing socially optimal output choices by non-cooperatively acting oligopolists. A decentralized mechanism is a vector of balanced transfers among firms determined as a function of firms’ output choices. The mechanism is devised by a regulator with a full knowledge of demand and without any knowledge of the firms’ cost functions. Restricting the set of admissible demand and cost functions such that the firms always have an incentive to produce, it turns out that the socially optimal solution is implementable insofar as the demand function is a polynomial of at most (n−1)th degree, n being the number of firms in the industry. The author is indebted to a referee and an associate editor for their helpful comments.     

Erratum to “Do pure indivisibilities prevent core equivalence? Core equivalence theorem in an atomless economy with purely indivisible commodities only” [J. Math. Econ. 41 (4–5) (2005) 571–601]

We consider a pure exchange economy with a continuum of agents and finitely many indivisible commodities. Every commodity can be consumed only in integer amounts. Thus, agents’ preferences are locally satiated and no commodity bundle has necessarily local cheaper points. We introduce a core which is an intermediate concept between the strong core and the weak core. In our economy, this core is the most natural concept in the sense that it coincides with the set of all exactly feasible Walras allocations.     

The Walras core of an economy and its limit theorem

The Walras core of an economy is the set of allocations that are attainable for the consumers when their trades are constrained to be based on some agreed price system, such that no alternative price system exists for any sub-coalition that allows all members to trade to something better. As compared with the Edgeworth core, both coalitional improvements and being a candidate allocation for the Walras core become harder. The Walras core may even contain allocations that violate the usual Pareto efficiency. Nevertheless, the competitive allocations are the same under the two theories, and the equal-treatment Walras core allocations converge under general conditions to the competitive allocations in the process of replication.     

Dynamics,stability, and foresight in the Shapley–Scarf housing market

While most of the literature starting with Shapley and Scarf (1974) have considered a static exchange economy with indivisibilities, this paper studies the dynamics of such an economy. We find that both the dynamics generated by competitive equilibrium and the one generated by the weak dominance relation, converge to a set of allocations we define as strictly stable, which we can show to exist. Moreover, we show that even when only pairwise exchanges between two traders are allowed, the strictly stable allocations are attained eventually if traders are sufficiently farsighted.     

Implementation of voting operators

We show that a theory of implementation can be developed in the Aizerman–Aleskerov framework, capturing the main ideas regarding Nash implementation in the Arrovian case. In fact we obtain the counterparts of the results of [Maskin, E., 1977. Nash Equilibrium and Welfare Optimality. MIT, Mimeo] and [Moore, J., Repullo, R., 1990. Nash implementation. A full characterization. Econometrica 58, 1038–1100] in the new framework.