Differential Information Economies Research Articles

New conditions for the existence of Radner equilibrium with infinitely many states

In atomless differential information economies, equilibria are known not to exist prevalently even when agents are risk averse expected utility maximizers. The notion of prevalence involves essentially picking an economy at random. In this paper, however, we establish existence results with economically meaningful assumptions on the information structure. We obtain existence when agents have independent information, and also when the total endowment of the economy is common knowledge.

The veto mechanism in atomic differential information economies

We establish new characterizations of Walrasian expectations equilibria based on the veto mechanism in the framework of differential information economies with a complete finite measure space of agents. We show that it is enough to consider the veto power of a single coalition, consisting of the entire set of agents, to obtain the Aubin private core. Moreover, we investigate on the veto power of arbitrarily small and big coalitions, providing an extension to mixed markets of well known Schmeidler (1972) and Vind’s (1972) results in terms of Aubin private core allocations.

Aggregate preferred correspondence and the existence of a maximin REE

A general model of a pure exchange differential information economy is studied. In this economic model, the space of states of nature is a complete probability measure space, the space of agents is a finite measure space, and the commodity space is the Euclidean space. Under some appropriate and standard assumptions on agents' characteristics, results on continuity and measurability of the aggregate preferred correspondence similar to that of Aumann [8] are established. These results together with other techniques are then employed to prove the existence of a maximin rational expectations equilibrium (maximin REE) of the economic model.

On fairness of equilibria in economies with differential information

The paper proposes a notion of fairness which overcomes the conflict arising between efficiency and the absence of envy in economies with uncertainty and asymmetrically informed agents. We do it in general economies which include, as particular cases, the main models of differential information economies, providing in this framework a natural competitive equilibrium notion which satisfies the fair criterion. The analysis is conducted allowing the presence of large traders, which may cause the lack of perfect competition.

Coalitional fairness in interim differential information economies

In this paper we propose a concept of coalitional fair allocation in order to solve the tension that may exist between efficiency and envy-freeness when agents are asymmetrically informed and the equity of allocations is evaluated at the interim stage.

Incentive compatibility with interdependent preferences

We introduce new concepts of incentive compatibility and efficiency for a differential information economy with interdependent preferences. Using the new definitions, we provide theorems on the consistency of efficiency and incentive compatibility.

Differential Information Economies: Contract Based Approach

Differential information economies are investigated from the viewpoint of contract based approach, developed in series of author’s papers. The key idea of the approach is to change the study of a “final” allocation of commodities with (different forms) stable webs of barter contracts which implement the allocation. This way main DIE equilibrium notions are clarified and the most significant kinds of core and domination are extracted and their conformity with Walrasian Expectations Equilibrium (WEE) and Rational Expectations Equilibrium (REE) is provided. The series of new concepts of core and domination and appropriate equilibrium notions are introduced: core and equilibrium with differentiated agents (well correspond to conditional expected utilities), interim core and equilibrium. The last one is closely related with REE-equilibrium and clarifies that is an appropriate core and kind of stability. There are proven new theorems on existence of core and quasi-equilibria.

Beauty Contests and Asset Prices under Asymmetric Information

In this paper, we study a dynamic Gaussian financial market model in which the traders form higher-order expectations about the fundamental value of a single risky asset. Rational uninformed traders are introduced into an otherwise standard differential information economy to investigate the impact of asymmetric information. In a two-period economy, there is a unique linear equilibrium; beauty contests under asymmetric information do not introduce excess volatility driven by self-fulfilling multiple equilibria. Under certain conditions, there is a nonmonotonic relationship between price volatility and the proportion of uninformed traders.

On mixed markets with asymmetric information

In asymmetric information exchange economies involving both non-negligible and negligible agents, one should expect the failure of the private Core-Walras Equivalence Theorem. This paper shows that if “large” traders are similar to each other, then they lose their market power and hence the Equivalence Theorem can be restored. We also investigate on weaker equivalences among Walrasian expectations allocations, Aubin private core and private core allocations of the original mixed economy and the atomless one associated to it, without the assumption that all atoms are of the same type. Furthermore, extensions of Herves-Moreno-Yannelis and Schmeidler Theorems (compare Herves et al. in J Math Econ 41:844–856, 2005a; Schemidler in Econometrica 40:579–580, 1972) are given for differential information economies in which the feasibility constraints are imposed with an equality (exact feasibility).

Equilibrium theory with asymmetric information and infinitely many states

Radner (Econometrica 36, 31–58 1968) proved existence of a competitive equilibrium for differential information economies with finitely many states. We extend this result to economies with infinitely many states of nature. Each agent observes a public and a private signal. The publicly observed signal may take infinitely many values but, in order to get existence, we assume that private signals only take finitely many values. Actually, there is no hope to get a general existence result since Podczeck et al. (Vienna University Working Papers 2008) already proposed non-existence results.

Theorems on the core of an economy with infinitely many commodities and consumers

It is known that the classical theorems of Grodal [Grodal, B., 1972. A second remark on the core of an atomless economy. Econometrica 40, 581–583] and Schmeidler [Schmeidler, D., 1972. A remark on the core of an atomless economy. Econometrica 40, 579–580] on the veto power of small coalitions in finite dimensional, atomless economies can be extended (with some minor modifications) to include the case of countably many commodities. This paper presents a further extension of these results to include the case of uncountably many commodities. We also extend Vind’s [Vind, K., 1972. A third remark on the core of an atomless economy. Econometrica 40, 585–586] classical theorem on the veto power of big coalitions in finite dimensional, atomless economies to include the case of an arbitrary number of commodities. In another result, we show that in the coalitional economy defined by an atomless individualistic model, core–Walras equivalence holds even if the commodity space is non-separable. The above-mentioned results are also valid for a differential information economy with a finite state space. We also extend Kannai’s [Kannai, Y., 1970. Continuity properties of the core of a market. Econometrica 38, 791–815] theorem on the continuity of the core of a finite dimensional, large economy to include the case of an arbitrary number of commodities. All of our results are applications of a lemma, that we prove here, about the set of aggregate alternatives available to a coalition. Throughout the paper, the commodity space is assumed to be an ordered Banach space which has an interior point in its positive cone.

The measure of blocking coalitions in differential information economies

We provide an evaluation of the measure of privately blocking coalitions in differential information economies. In the case of atomless economies, it is proved that for a Pareto optimal allocation that is not a Walrasian expectations equilibrium, to any symmetric profile there corresponds a ball such that "almost half” of the profiles it contains are privately blocking. Analogous results are proved in the case of finite differential information economies for generalized coalitions and social coalition structures. From a different point of view, the paper can be considered as a contribution showing private core equivalence theorems under restrictions on coalition formation.

A market game approach to differential information economies

In this paper we recast a differential information economy as a strategic game in which players propose net trades and prices. Pure strategy Nash equilibria are strong and determine both consumption plans and commodity prices that coincide with the Walrasian Expectations equilibria of the underlying economy.

Characterization and incentive compatibility of Walrasian expectations equilibrium in infinite dimensional commodity spaces

We consider a differential information economy with infinitely many commodities and analyze the veto power of the grand coalition with respect the ability of blocking non-Walrasian expectations equilibrium allocations. We provide two different Walrasian expectations equilibrium equivalence results. First by perturbing the initial endowments in a precise direction we show that an allocation is a Walrasian expectations equilibrium if and only if it is not “privately dominated” by the grand coalition. The second characterization deals with the fuzzy veto in the sense of Aubin but within a differential information setting. This second equivalence result provides a different characterization for the Walrasian expectations equilibrium and shows that the grand coalition privately blocks in the sense of Aubin any non Walrasian expectations equilibrium allocation with endowment participation rate arbitrarily close to the total initial endowment participation for every individual. Finally, we show that any no free disposal Walrasian expectations equilibria is coalitional Bayesian incentive compatible. Since the deterministic Arrow-Debreu-McKenzie model is a special case of the differential information economy model, one derives new characterizations of the Walrasian equilibria in economies with infinitely many commodities.

The Aubin private core of differential information economies

We establish characterizations of Radner equilibrium allocations via private core notions in the framework of differential information economies with a finite number of states of nature and a measure space of agents that may have atoms. The commodity space is an ordered separable Banach space whose positive cone admits an interior point. We introduce the notion of Aubin private core and prove that it provides a characterization of Radner equilibrium allocations. We show that the Aubin private core is equivalent to Edgeworth private equilibria and to privately non-dominated allocations of suitable associated economies. Mathematics Subject Classification (2000): 91B50, 91B44 Journal of Economic Literature Classification: D51, D82, D11

An equivalence theorem for a differential information economy

In a pure exchange economy with differential information and a finite set of traders, physical commodities and states of nature, we characterize the Walrasian expectations or Radner equilibria by using the veto power of the grand coalition. We prove that an allocation x is a Radner equilibrium allocation if and only if it is “privately non-dominated” by the grand coalition in every economy obtained by perturbing the original initial endowments in the direction of x. The first and second welfare theorems become particular cases of our main result. Since the deterministic Arrow–Debreu–McKenzie model is a special case of the differential information economy model we also provide a new characterization of the Walrasian equilibria.

On extensive form implementation of contracts in differential information economies

In the context of differential information economies, with and without free disposal, we consider the concepts of Radner equilibrium, rational expectations equilibrium, private core, weak fine core and weak fine value. We look into the possible implementation of these concepts as perfect Bayesian or sequential equilibria of noncooperative dynamic formulations. We construct relevant game trees which indicate the sequence of decisions and the information sets, and explain the rules for calculating ex ante expected payoffs. The possibility of implementing an allocation is related to whether or not it is incentive compatible. Implementation through an exogenous third party or an endogenous intermediary is also considered.

Coalition structure values in differential information economies: is unity a strength?

The coalition structure (CS) value, introduced by Owen [G. Owen, Values of games with a priori unions, in: Essays in Mathematical Economics and Game Theory, Springer Verlag, Berlin, 1977] and Hart and Kurz [Econometrica 51 (1983) 1047], generalizes the Shapley value to social situations where coalitions form for the purpose of bargaining. This paper introduces the CS value to economies with differential information. We show that the private CS values exists and is Bayesian incentive compatible. Moreover, we construct examples that go against the intuitive viewpoint that “unity is strength”. In particular, we consider a three-person economy in which two agents bargain as a unit against the third agent. We show that bargaining as a unit is advantageous if and only if information is complete. This result sheds new light on bargaining under differential information.

The Ex Ante Incentive Compatible Core in the Absence of Wealth Effects

In a differential information economy with quasi-linear utilities, monetary transfers facilitate the fulfillment of incentive compatibility constraints: the associated ex ante core is generically non-empty. However, we exhibit a wellbehaved exchange economy in which this core is empty, even if goods are allocated through random mechanisms.

Coalitional Bayesian Nash implementation in differential information economies

Coalitional Bayesian Nash implementation in differential information economies