A Characterization of Strategic Complementarities

I characterize games for which there is an order on strategies such that the game has strategic complementarities. I prove that, with some qualifications, games with a unique equilibrium have complementarities if and only if Cournot best-response dynamics has no cycles; and that all games with multiple equilibria have complementarities. This is a negative result because it implies that the predictive power of complementarities alone is very weak. As an application of my results I show that generic 2 X 2 games either have no pure-strategy equilibria, or are GSC.

A Characterization of Strategic Complementarities

I characterize games for which there is an order on strategies such that the game has strategic complementarities. I prove that, with some qualifications, games with a unique equilibrium have complementarities if and only if Cournot best-response dynamics has no cycles; and that all games with multiple equilibria have complementarities. As applications of my results, I show: 1. That generic 2X2 games either have no pure-strategy equilibria, or have complementarities. 2. That generic two-player infinite ordinal potential games have complementarities

A characterization of strategic complementarities

I characterize games for which there is an order on strategies such that the game has strategic complementarities. I prove that, with some qualications, games with a unique equilibrium have complementarities if and only if Cournot best-response dynamics has no cycles; and that all games with multiple equi- libria have complementarities. As applications of my results, I show: 1. That generic 2X2 games either have no pure-strategy equilibria, or have complementarities. 2. That generic two-player nite ordinal potential games have complementarities.Strategic complementarities, supermodular games, non-standard analysis, Cournot best-response dynamics, potential games.

The convergence of fictitious play in games with strategic complementarities: A Comment

In a recent article, Hahn [Hahn, S. (2008). The convergence of fictitious play in games with strategic complementarities. Economics Letters 99, 2, 304-306] claims to prove convergence of fictitious play in games with strategic complementarities. I show here that the proof is flawed and convergence remains an open question.Fictitious play; Strategic complementarities; Supermodular games

A non-robustness in the order structure of the equilibrium set in lattice games

The order and lattice structure of the equilibrium set in games with strategic complements do not survive a minimal introduction of strategic substitutes: in a lattice game in which all-but-one players exhibit strategic complements (with one player exhibiting strict strategic complements), and the remaining player exhibits strict strategic substitutes, no two equilibria are comparable. More generally, in a lattice game, if either (1) just one player has strict strategic complements and another player has strict strategic substitutes, or (2) just one player has strict strategic substitutes and has singleton-valued best-responses, then without any restrictions on the strategic interaction among the other players, no two equilibria are comparable. In such cases, the equilibrium set is a non-empty, complete lattice, if, and only if, there is a unique equilibrium. Moreover, in such cases, with linearly ordered strategy spaces, the game has at most one symmetric equilibrium. Several examples are presented.Lattice games, strategic complements, strategic substitutes, equilibrium set

Extensive-form games and strategic complementarities

I prove the subgame-perfect equivalent of the basic result for Nash equilibria in normal-form games of strategic complements: the set of subgame-perfect equilibria is a nonempty, complete lattice—in particular, subgame-perfect Nash equilibria exist. For this purpose I introduce a device that allows the study of the set of subgame-perfect equilibria as the set of fixed points of a correspondence. My results are limited because extensive-form games of strategic complementarities turn out—surprisingly—to be a very restrictive class of games

A unified approach to comparative statics puzzles in experiments

Many experimental studies implement two versions of one game for which agents’ behavior is fundamentally different even though the Nash prediction is the same. This paper provides a novel explanation of such findings. Starting from the observation that many of the games under consideration satisfy the strategic-complementarity property, I obtain predictions for the direction of adjustment in response to parameter changes which do not require calculation of the equilibrium. I show that these predictions explain the experimental evidence very well. Further, I provide a behavioral justification of the approach, and I explore the relation to alternative explanations based on equilibrium selection theories and the quantal response equilibrium.experimental economics, game theory, Nash equilibrium, embedding method

The convergence of fictitious play in games with strategic complementarities: A Comment

In a recent article, Hahn [Hahn, S. (2008). The convergence of fictitious play in games with strategic complementarities. Economics Letters 99, 2, 304-306] claims to prove convergence of fictitious play in games with strategic complementarities. I show here that the proof is flawed and convergence remains an open question

Endogenous Heterogeneity in Strategic Models: Symmetry-breaking via Strategic Substitutes and Nonconcavities

This paper is an attempt to develop a unified approach to endogenous heterogeneity by constructing general class of two-player symmetric games that always possess only asymmetric pure-strategy Nash equilibria. These classes of games are characterized in some abstract sense by two general properties: payo? non-concavities and some form of strategic substitutability. We provide a detailed discussion of the relationship of this work with Matsuyama’s symmetry breaking framework and with business strategy literature. Our framework generalizes a number of models dealing with two-stage games, with long term investment decisions in the first stage and product market competition in the second stage. We present the main examples that motivate this study to illustrate the generality of our approach.firm heterogeneity; submodular games; business strategy; innovation strategies.