Efficient and stable collective choices under gregarious preferences

We consider collective choice problems where a set of agents have to choose an alternative from a finite set and agents may or may not become users of the chosen alternative. An allocation is a pair given by the chosen alternative and the set of its users. Agents have gregarious preferences over allocations: given an allocation, they prefer that the set of users becomes larger. We require that the final allocation be efficient and stable (no agent can be forced to be a user and no agent who wants to be a user can be excluded). We propose a two-stage sequential mechanism whose unique subgame perfect equilibrium outcome is an efficient and stable allocation which also satisfies a maximal participation property.     

Stable Assignment of Public Facilities under Congestion

We study the problem of locating multiple public facilities when each member of society has to be assigned to exactly one of these facilities. Individuals' preferences are assumed to be single‐peaked over the interval of possible locations and negatively affected by congestion. We characterize strategy‐proof, efficient, and stable allocation rules when agents have to be partitioned between two groups of users and discuss the normative content of the stability property. Finally we prove that when more than two groups have to be formed, even with common information on the distribution of the peaks, there is no strategy‐proof, efficient, and stable allocation rule.     

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.     

Mechanism design with partial state verifiability

We study implementation in environments where agents have limited ability to imitate others. Agents are randomly and privately endowed with type-dependent sets of messages. So sending a message becomes a partial proof regarding type. For environments where agents can send any combination of available messages, we develop an Extended Revelation Principle and characterize the incentive constraints which implementable allocations must satisfy. When not all message combinations are feasible, static mechanisms no longer suffice. If a ‘punishment’ allocation exists for each agent, then implementable allocations can be characterized as equilibria of a “Revelation Game,” in which agents first select from the menus of allocation rules, then the mediator requests each agent to send some verifying messages. When a punishment allocation fails to exist for some agent, dynamic games in which agents gradually reveal their evidence implement a larger set of outcomes. The latter result provides a foundation for a theory of debate.     

The Dynamic Vickrey Auction

We study the efficient allocation of a single object over a finite time horizon. Buyers arrive randomly over time, are long-lived, and have independent private values. The valuation of a buyer may depend on the time of the allocation in an arbitrary way. We construct an incentive compatible mechanism in which (A) there is a single financial transaction (with the buyer), (B) ex-post participation constraints are fulfilled, (C) there is no positive transfer to any agent and (D) payments are determined online. We exploit that under the efficient allocation rule, there is a unique potential winning period for each buyer. This reduces the multidimensional type to one dimension and the payment of the winner can be defined as the lowest valuation for the potential winning period, with which the buyer would have won the object. In a static model, this payment rule coincides with the payment rule of the Vickrey Auction.     

Mechanism design with partial state verifiability

We study implementation in environments where agents have limited ability to imitate others. Agents are randomly and privately endowed with type-dependent sets of messages. So sending a message becomes a partial proof regarding type. For environments where agents can send any combination of available messages, we develop an Extended Revelation Principle and characterize the incentive constraints which implementable allocations must satisfy. When not all message combinations are feasible, static mechanisms no longer suffice. If a ‘punishment’ allocation exists for each agent, then implementable allocations can be characterized as equilibria of a “Revelation Game,” in which agents first select from the menus of allocation rules, then the mediator requests each agent to send some verifying messages. When a punishment allocation fails to exist for some agent, dynamic games in which agents gradually reveal their evidence implement a larger set of outcomes. The latter result provides a foundation for a theory of debate.     

Decreasing absolute prudence: Characterization and applications to second-best risk sharing

In this paper, we provide two basic properties of utility functions u which exhibit decreasing absolute prudence i.e. (− u/u″)′ ≤ 0. These properties are used to examine the allocation of risks in an economy when some agents bear non-transferable risks. We show that it is fair Pareto-efficient to let those with a non-transferable risk bear relatively less of the transferable risk in the economy if and only if absolute prudence is decreasing. In another model, there is a complete set of contingent markets, but some agents have no direct access to them. We examine the fair efficient allocation of risk in a pool gathering a trader and a non-trader. Decreasing absolute prudence provides an upper bound to the share of the pool's risk that should be borne by the trader.     

Production-inventory games: A new class of totally balanced combinatorial optimization games

In this paper we introduce a new class of cooperative games that arise from production-inventory problems. Several agents have to cover their demand over a finite time horizon and shortages are allowed. Each agent has its own unit production, inventory-holding and backlogging cost. Cooperation among agents is given by sharing production processes and warehouse facilities: agents in a coalition produce with the cheapest production cost and store with the cheapest inventory cost. We prove that the resulting cooperative game is totally balanced and the Owen set reduces to a singleton: the Owen point. Based on this type of allocation we find a population monotonic allocation scheme for this class of games. Finally, we point out the relationship of the Owen point with other well-known allocation rules such as the nucleolus and the Shapley value.     

Achieving efficiency with manipulative bargainers

Two agents bargain over the allocation of a bundle of divisible commodities. After strategically reporting utility functions to a neutral arbitrator, the outcome is decided by using a bargaining solution concept chosen from a family that includes the Nash and the Raiffa–Kalai–Smorodinsky solutions. When reports are restricted to be continuous, strictly increasing and concave, it has been shown that this kind of “distortion game” leads to inefficient outcomes. We study the distortion game originated when agents are also allowed to claim non-concave utility functions. Contrasting with the previous literature, any interior equilibrium outcome is efficient and any efficient allocation can be supported as an equilibrium outcome of the distortion game. In a similar fashion to the Nash demand game we consider some uncertainty about the opponent's features to virtually implement the Nash bargaining solution.     

Price stabilizing, Pareto improving policies

One possible justification for a stabilization policy is that there is volatility in macro variables that individual agents cannot insure against. We study the simplest possible extension of the stochastic two-period, one agent and one commodity OLG model, where we have added one more period, with only one potential activity, namely, trading of contingent commodities. We assume, however, that markets are incomplete. In this case the Monetary equilibrium is not Pareto Optimal and for an open set of economies an allocation where fluctuations in realized savings are removed, Pareto dominates the monetary equilibrium. This allocation may be implemented by means of a monetary/fiscal policy. The policy considered has a simple rationale, namely that it removes some of the uncertainty that agents face by reducing price, i.e interest rate volatility. We consider two fundamental sources of such volatility, namely, respectively an objective and a subjective signal about the distribution of future endowments. The first case is when agents have rational expectations while the second case is studied in the context of agents having rational beliefs, beliefs which are consistent with empirical observations but not (necessarily) correct.     

Pigouvian Taxes in General Equilibrium with a Fixed Tax Redistribution Rule

This paper establishes existence of a first-best emission tax in a general equilibrium model with pollution, when the redistribution rule of the tax income is chosen fixed and independently of the Pigouvian tax rate. It is known that under standard convexity assumptions each Pareto efficient allocation can be implemented by simultaneously choosing a Pigouvian tax rate and an appropriate lump sum redistribution of income. In real politics, however, tax redistribution schemes are often restricted to a small feasible set. Nonetheless we show that for any given lump sum redistribution rule, being continuous in overall tax income, an emission tax rate exists that leads to a Pareto efficient equilibrium.     

Fair allocations of a renewable resource

In an economy with finitely many agents, one renewable resource, and an infinite horizon, it is shown that there is exactly one maximal allocation corresponding to given limiting shares of consumption and this allocation converges monotonically. Therefore, if there is no discounting, at most one fair maximal program exists—that which gives an equal amount to each individual in the limit. In this allocation, envy is always finite. However, only in special cases is it envyfree. This is in contrast to the case of finite economies where envy-free and Pareto efficient allocations may not exist or, if they exist, may not be unique.     

Hidden information,bargaining power,and efficiency: an experiment

We devise an experiment to explore the effect of different degrees of bargaining power on the design and the selection of contracts in a hidden-information context. In our benchmark case, each principal is matched with one agent of unknown type. In our second treatment, a principal can select one of three agents, while in a third treatment an agent may choose between the contract menus offered by two principals. We first show theoretically how different ratios of principals and agents affect outcomes and efficiency. Informational asymmetries generate inefficiency. In an environment where principals compete against each other to hire agents, these inefficiencies may disappear, but they are insensitive to the number of principals. In contrast, when agents compete to be hired, efficiency improves dramatically, and it increases in the relative number of agents because competition reduces the agents’ informational monopoly power. However, this environment also generates a high inequality level and is characterized by multiple equilibria. In general, there is a fairly high degree of correspondence between the theoretical predictions and the contract menus actually chosen in each treatment. There is, however, a tendency to choose more ‘generous’ (and more efficient) contract menus over time. We find that competition leads to a substantially higher probability of trade, and that, overall, competition between agents generates the most efficient outcomes.     

Strategyproof and Nonbossy Multiple Assignments

We consider the allocation of heterogeneous indivisible objects without using monetary transfers. Each agent may be assigned more than one object. We show that an allocation rule is strategyproof, nonbossy, and satisfies citizen sovereignty if and only if it is a sequential dictatorship . In a sequential dictatorship agents are assigned their favorite objects that are still available, according to a sequentially endogenously determined hierarchy of the agents. We also establish that replacing nonbossiness by a stronger criterion restricts the characterized class of allocation rules to serial dictatorships , in which the hierarchy of the agents is fixed a priori.     

Behavioral explanations of efficient public good allocations

Theorists have studied decentralized allocation mechanisms by characterizing the Cournot-Nash equilibria of the mechanism. However, when a mechanism is operationalized by an iterative decision process, and agents derive utility only from the final outcome, Cournot behavior may not be an appropriate solution concept. We suggest two alternative behavioral models, reservation behavior and satisficing behavior, which recognize the impact of the iterative process upon incentives, yet maintain some of the critical simplifications that have made Cournot behavior an attractive model.We report on nine public good experiments with a Groves-Ledyard general equilibrium mechanism. Overall, the experiments attain highly efficient allocations, despite widespread violations of Cournot behavior. We suggest the explanation that most subjects initially followed reservation behavior, and then came to adopt satisficing behavior.     

Cardinal Bayesian allocation mechanisms without transfers

In allocating goods with no use of monetary transfers, random allocation mechanisms can be designed in order to elicit information on preference intensities. I study the nontransfer allocation of two ex-ante identical objects under Bayesian incentive compatibility, with symmetric agents and independent private valuations. I find the ex-ante utilitarian-optimal mechanism, in which the probability of receiving a specified object is used as “numeraire” to purchase probability units of the other object. I characterize this mechanism as an appropriate combination of lotteries, auctions and insurance. The latter element ensures that efficient auctions are feasible. If the problem is constrained to guarantee exactly one object per agent, then the optimal mechanism uses no information other than the agents? ordinal preferences.     

Efficient resource allocation under multi-unit demand

We study resource allocation with multi-unit demand, such as the allocation of courses to students. In contrast to the case of single-unit demand, no stable mechanism, not even the (student-proposing) deferred acceptance algorithm, achieves desirable properties: it is not strategy-proof and the resulting allocation is not even weakly efficient under submitted preferences. We characterize the priority structure of courses over students under which stability is consistent with strategy-proofness or efficiency. We show that stability is compatible with strategy-proofness or efficiency if and only if the priority structure is essentially homogeneous. This result suggests that efficient allocation under multi-unit demand is difficult and that the use of stable mechanisms may not deliver desirable outcomes.     

Strongly stable networks

We analyze the formation of networks among individuals. In particular, we examine the existence of networks that are stable against changes in links by any coalition of individuals. We show that to investigate the existence of such strongly stable networks one can restrict focus on a component-wise egalitarian allocation of value. We show that when such strongly stable networks exist they coincide with the set of efficient networks (those maximizing the total productive value). We show that the existence of strongly stable networks is equivalent to core existence in a derived cooperative game and use that result to characterize the class of value functions for which there exist strongly stable networks via a “top convexity” condition on the value function on networks. We also consider a variation on strong stability where players can make side payments, and examine situations where value functions may be non-anonymous—depending on player labels.     

Serial dictatorship and Pareto optimality

In a deterministic allocation problem in which each agent is entitled to receive exactly one object, an allocation is Pareto optimal if and only if it is the outcome of a serial dictatorship. We extend the definition of serial dictatorship to settings in which some agents may be entitled to receive more than one object, and study the efficiency and uniqueness properties of the equilibrium allocations. We prove that subgame perfect equilibrium allocations of serial dictatorship games are not necessarily Pareto optimal; and generally not all Pareto optima can be implemented as subgame perfect equilibrium allocations of serial dictatorship games, except in the 2-agent separable preference case. Moreover, serial dictatorship games do not necessarily have unique subgame perfect equilibrium allocations, except in the 2-agent case, hence their outcomes are indeterminate and manipulable.     

The (sub-)optimality of the majority rule

We consider collective choice from two alternatives. Ex-ante, each agent is uncertain about which alternative she prefers, and may be uncertain about the intensity of her preferences. An environment is given by a probability distribution over utility vectors that is symmetric across agents and neutral across alternatives. In many environments, the majority voting rule maximizes agents? ex-ante expected utilities among all anonymous and dominant-strategy implementable choice rules. But in some environments where the agents? utilities are stochastically correlated, other dominant-strategy choice rules are better for all agents. If utilities are stochastically independent across agents, majority voting is ex-ante optimal among all anonymous and incentive-compatible rules. We also compare rules from an interim-viewpoint.