Set Of Equilibrium Payoffs Research Articles

Nash Equilibrium for Differential Games and Nonanticipative Strategies

AbstractIn this paper we introduce the definition of Nash equilibrium of two-person nonzero-sum differential in the class of nonanticipative strategies. It is assumed that both players play in nonanticipative strategies. We characterize the set of Nash equilibrium payoffs for this situation also.

An Algorithm for Two Player Repeated Games with Perfect Monitoring

Consider repeated two-player games with perfect information and discounting. We provide an algorithm that computes the set of payoff pairs V* of all pure strategy subgame perfect equilibria with public randomization. The algorithm provides significant efficiency gains over the existing implementations of the algorithm from Abreu, Pearce and Stacchetti (1990). These efficiency gains arise from a better understanding of the manner in which extreme points of the equilibrium payoff set are generated. An important theoretical implication of our algorithm is that the set of extreme points E of V* is finite. Indeed, |E| ≤ 3|A|, where A is the set of action profiles of the stage game.

Recursive Methods in Discounted Stochastic Games: An Algorithm for δ → 1 and a Folk Theorem

We present an algorithm to compute the set of perfect public equilibrium payoffs as the discount factor tends to one for stochastic games with observable states and public (but not necessarily perfect) monitoring when the limiting set of (long-run players’) equilibrium payoffs is independent of the initial state. This is the case, for instance, if the Markov chain induced by any Markov strategy profile is irreducible. We then provide conditions under which a folk theorem obtains: if in each state the joint distribution over the public signal and next period’s state satisfies some rank condition, every feasible payoff vector above the minmax payoff is sustained by a perfect public equilibrium with low discounting.

Equilibrium payoffs of finite games

Abstract We study the structure of the set of equilibrium payoffs in finite games, both for Nash and correlated equilibria. In the two-player case, we obtain a full characterization: if U and P are subsets of R 2 , then there exists a bimatrix game whose sets of Nash and correlated equilibrium payoffs are, respectively, U and P, if and only if U is a finite union of rectangles, P is a polytope, and P contains U. The n-player case and the robustness of the result to perturbation of the payoff matrices are also studied. We show that arbitrarily close games may have arbitrarily different sets of equilibrium payoffs. All existence proofs are constructive.

Commodity Money with Frequent Search

A prominent feature of the Kiyotaki and Wright (1989) model of commodity money is the multiplicity of dynamic equilibria. We show that the frequency of search is strongly related to the extent of multiplicity. To isolate the role of frequency of search in generating multiplicity, we (i) vary the frequency of search without changing the frequency of finding a trading partner and (ii) focus on symmetric dynamic equilibria, a class for which we can sharply characterize several features of the set of equilibria. For any finite frequency of search this class retains much of the multiplicity. For each frequency we characterize the full set of equilibrium payoffs, strategies played, and dynamic paths of the state variables. Indexed by any of these features, the set of equilibria converges uniformly to a unique equilibrium in the continuous search limit. We conclude that when search is frequent, the seemingly exotic dynamics are irrelevant.

The Role of Commitment in Bilateral Trade

This paper solves for the set of equilibrium payoffs in bargaining with interdependent values when the informed party makes all offers, as discounting vanishes. The seller of a good is informed of its quality, which affects both his cost and the buyer's valuation, but the buyer is not. To characterize this payoff set, we derive an upper bound, using mechanism design with limited commitment. We then prove that this upper bound is tight, by showing that all its extreme points are equilibrium payoffs. Our results shed light on the role of different forms of commitment on the bargaining process. In particular, we show that it is the buyer's inability to commit to a contract before observing the terms of trade that precludes efficiency.

Information can wreck cooperation: A counterpoint to Kandori (1992)

We propose a simple model of repeated games with private monitoring and time-varying information structures. We then obtain an example demonstrating that the set of achievable equilibrium payoffs may shrink when players' information regarding opponents' information structures is increased.

The use of public randomization in discounted repeated games

This paper presents an example where the set of subgame-perfect equilibrium payoffs of the infinitely repeated game without public randomization is not convex, no matter how large the discount factor is. Also, the set of pure-strategy equilibrium payoffs is not monotonic with respect to the discount factor in this example. These results are in sharp contrast to the fact that the equilibrium payoff set is convex and monotonic if public randomization is available.

Folk Theorem with a Continuum of Public Signals

We extend Fudenberg and Levine’s (1994) characterization of the limit set of perfect public equilibrium payoffs of repeated games with imperfect public monitoring as the discount factor approaches one to that of repeated games in which the set of public signals is a continuum. Using this characterization, we provide folk theorems requiring full rank conditions that imply the satisfaction of the conditions of Fudenberg et al.(1994) in an associated game with a finite set of public signals. We finally apply a folk theorem to the analysis of collusion among firms in an oligopoly considered by Green and Porter (1984).

Unattainable Payoffs for Repeated Games of Private Monitoring

We tightly bound from the outside the set of sequential equilibrium payoffs in repeated games of private monitoring. To do this, we develop a tractable new solution concept for standard repeated games with perfect monitoring: Markov Perfect Correlated Equilibrium generalizes the operator approach of Abreu, Pearce, and Stacchetti (1990), but instead takes correlated equilibrium of the auxiliary game. We show that for any private monitoring structure, the set of sequential equilibrium payoffs of a repeated game is contained within the set of Markov Perfect Correlated Equilibrium payoffs of the repeated expected game. This bound can be made tight with a simple two-stage procedure. The techniques we develop are tractable and shed light on all economic settings with imperfectly observed actions, like dynamic oligopoly, long-term partnerships, and relational contracting. In all cases, they yield the sharpest equilibrium payoff prediction that is agnostic about the monitoring structure.

Selecting equilibria in common agency games

We characterize equilibrium payoffs of a delegated common agency game in a public good context where principals use smooth contribution schedules. We prove that under complete information, payoff vectors of equilibria with truthful schedules coincide with the set of smooth equilibrium payoffs, including non-truthful schedules. We next consider whether the presence of arbitrarily small amounts of asymmetric information is enough to refine this payoff set. Providing that the extensions of the equilibrium schedules beyond the equilibrium point are flatter than truthful schedules, the set of equilibrium payoffs is strictly smaller than the set of smooth (equivalently, truthful) equilibrium payoffs. Interestingly, some forms of asymmetric information do not sufficiently constrain the slopes of the extensions and fail to refine the payoff set. In the case of a uniform distribution of types and arbitrary out-of-equilibrium contributions, the refinement has no bite. If, however, one restricts out-of-equilibrium behavior in a natural way, the refinement is effective. Alternatively, we may consider an exponential distribution with unbounded support (and hence no out-of-equilibrium choices) and we find that the refinement selects a unique equilibrium payoff vector equal to Lindahl prices. As a separate contribution, equilibria with forcing contracts are also considered both under complete and asymmetric information.

The optimal degree of cooperation in the repeated Prisoners' Dilemma with side payments

In the infinitely repeated Prisoners' Dilemma with side payments, we characterize the Pareto frontier of the set of subgame perfect equilibrium payoffs for all possible combinations of discount factors. Play paths implementing Pareto dominant equilibrium payoffs are uniquely determined in all but the first period. Full cooperation does not necessarily implement these payoffs even when it maximizes total stage game payoffs. Rather, when the difference in players' discount factors is sufficiently large, Pareto dominant equilibrium payoffs are implemented by partial cooperation supported by repeated payments from the impatient to the patient player. When both players are sufficiently patient, such payoffs, while implemented via full cooperation, are supported by repeated payments from the impatient to the patient player. We characterize conditions under which public randomization has no impact on the Pareto dominant equilibrium payoffs and conditions under which such payoffs are robust to renegotiation.

Coordinating under incomplete information

We show that, in a minimum effort game with incomplete information where player types are independently drawn, there is a largest and smallest Bayesian equilibrium, leading to the set of equilibrium payoffs (as evaluated at the interim stage) having a lattice structure. Furthermore, the range of equilibrium payoffs converges to those of the deterministic complete information version of the game, in the limit as the incomplete information vanishes. This entails that such incomplete information alone cannot explain the equilibrium selection suggested by experimental evidence.

A limit characterization of belief-free equilibrium payoffs in repeated games

The present paper studies repeated games with private monitoring, and characterizes the set of belief-free equilibrium payoffs in the limit as the discount factor approaches one and the noise on private information vanishes. Contrary to the conjecture by Ely et al. [J.C. Ely, J. Hörner, W. Olszewski, Belief-free equilibria in repeated games, Econometrica 73 (2005) 377–415], the equilibrium payoff set is computed by the same formula, no matter how many players there are. As an application of this result, a version of the folk theorem is established for N-player prisoner's dilemma games.

Multimarket contact in continuous-time games

This paper investigates whether multimarket contact is effective in increasing the value of collusion. We show that for any discount rate, the set of equilibrium payoffs (average per market) expands through multimarket contact in continuous-time games.

Forgiving-Proof Equilibrium in Infinitely Repeated Games

In repeated games, equilibrium often requires that any deviation be punished in the continuation, regardless of whether it is beneficial to the other players. It seems against the nature of non-cooperative game theory for the other players to decide what to do based on what one player did, rather than on the well-being of themselves. We introduce a new solution concept called a forgiving-proof equilibrium that recommends continuing as if nothing had happened after a player deviates without harming the others. A folk theorem is established to characterize the set of forgiving-proof equilibrium payoffs when players are sufficiently patient. The concept of forgiving-proof equilibrium significantly reduces the set of equilibrium outcomes in many repeated games.

On effective minimax payoffs and unequal discounting

We show that the folk theorem in Wen [Q. Wen (1994), The “Folk Theorem” for repeated games with complete information, Econometrica, 62, 949–954.] may not fully characterize the subgame perfect equilibrium payoff set in a repeated game with unequal discounting, where a player's equilibrium payoff could be strictly less than her effective minimax payoff.

A Minority Game with Bounded Recall

This paper studies a repeated minority game with public signals, symmetric bounded recall, and pure strategies. We investigate both public and private equilibria of the game with fixed recall size. We first show how public equilibria in such a repeated game can be represented as colored subgraphs of a de Bruijn graph. Then we prove that the set of public equilibrium payoffs with bounded recall converges to the set of uniform equilibrium payoffs as the size of the recall increases. We also show that private equilibria behave badly: A private equilibrium payoff with bounded recall need not be a uniform equilibrium payoff.

Repeated games with present-biased preferences

We study infinitely repeated games with perfect monitoring, where players have β – δ preferences. We compute the continuation payoff set using recursive techniques and then characterize equilibrium payoffs. We then explore the cost of the present-time bias, producing comparative statics. Unless the minimax outcome is a Nash equilibrium of the stage game, the equilibrium payoff set is not monotonic in β or δ . Finally, we show how the equilibrium payoff set is contained in that of a repeated game with smaller discount factor.

Perfect public equilibrium when players are patient

We provide a characterization of the limit set of perfect public equilibrium payoffs of repeated games with imperfect public monitoring as the discount factor goes to one. Our result covers general stage games including those that fail a “full-dimensionality” condition that had been imposed in past work. It also provides a characterization of the limit set when the strategies are restricted in a way that endogenously makes the full-dimensionality condition fail, as in the strongly symmetric equilibrium studied by Abreu [Abreu, D., 1986. Extremal equilibria of oligopolistic supergames. J. Econ. Theory 39, 191–228] and Abreu et al. [Abreu, D., Pearce, D., Stacchetti, E., 1986. Optimal cartel equilibria with imperfect monitoring. J. Econ. Theory 39, 251–269]. Finally, we use our characterization to give a sufficient condition for the exact achievability of first-best outcomes. Equilibria of this type, for which all continuation payoffs lie on the Pareto frontier, have a strong renegotiation-proofness property: regardless of the history, players can never unanimously prefer another equilibrium.