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Game Theory for Applied Economists【Robert Gibbons】.pdf

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Contents
Preface
1 Static Games of Complete Information
1.1 Basic Theory: Normal-Form Games and Nash Equilibrium
1.2 Applications
1.3 Advanced Theory
1.4 Further Reading
1.5 Problems
1.6 References
2 Dynamic Games of Complete Information
2.1 Dynamic Games of Complete and Perfect Information
2.2 Two-Stage Games of Complete but Imperfect Information
2.3 Repeated Games
2.4 Dynamic Games of Complete but Imperfect Information
2.5 Further Reading
2.6 Problems
2.7 References
3 Static Games of Incomplete Information
3.1 Theory: Static Bayesian Games and Bayesian Nash Equilibrium
3.2 Applications
3.3 The Revelation Principle
3.4 Further Reading
3.5 Problems
3.6 References
4 Dynamic Games of Incomplete Information
4.1 Introduction to Perfect Bayesian Equilibrium
4.2 Signaling Games
4.3 Other Applications of Perfect Bayesian Equilibrium
4.4 Refinements of Perfect Bayesian Equilibrium
4.5 Further Reading
4.6 Problems
4.7 References
Index
Game Theory for Applied Economists Robert Gibbons Princeton University Press Princeton, New Jersey
Contents 1 Static Games of Complete Information 1.1 Basic Theory: Normal-Form Games and Nash Equilibrium. . . . . . . . . . . . . . . . . . . . . 1.1.A Normal-Form Representation of Games. 1.1.B Iterated Elimination of Strictly Dominated Strategies . . . . . . . . . . . . . . . . . . . 1 2 2 1.2 Applications . . . . . . . . 4 1.1.C Motivation and Definition of Nash Equilibrium 8 14 14 21 22 27 1.2.A Coumot Model of Duopoly 1.2.B Bertrand Model of Duopoly 1.2.C Final-Offer Arbitration . . . 1.2.D The Problem of the Commons 1.3 Advanced Theory: Mixed Strategies and . . . . . . . . Existence of Equilibrium 1.3.A Mixed Strategies . . . . . . . . . 1.3.B Existence of Nash Equilibrium . 1.4 Further Reading 1.5 Problems 1.6 References ... 2 Dynamic Games of Complete Information 2.1 Dynamic Games of Complete and Perfect 29 29 33 48 48 51 55 57 Information. . . . . . . . . . . . . . . . 2.1.A Theory: Backwards Induction . . . 57 2.1.B Stackelberg Model of Duopoly. . . 61 2.1.C Wages and Employment in a Unionized Firm 64 68 2.1.D Sequential Bargaining . . . . . . . . . . 2.2 Two-Stage Games of Complete but Imperfect Information. . . . . . . . . . . . . . . . . . . . 71
viii CONTENTS 2.2.A Theory: Subgame Perfection . 2.2.B Bank Runs . . . . . . . . . . . 2.2.C Tariffs and Imperfect International Competition 2.2.D Tournaments . 2.3 Repeated Games . . . 2.3.A Theory: Two-Stage Repeated Games 2.3.B Theory: Infinitely Repeated Games 2.3.C Collusion between Coumot Duopolists . 2.3.0 Efficiency Wages . . .. . . . . . 2.3.E Time-Consistent Monetary Policy 2.4 Dynamic Games of Complete but Imperfect Information. . . . . . . . . . . 2.4.A Extensive-Form Representation of Games 2.4.B Subgame-Perfect Nash Equilibrium 2.5 Further Reading 2.6 Problems 2.7 References . . . . . . . 3 Static Games of Incomplete Information 71 73 75 79 82 82 88 . 102 . 107 112 115 115 . 122 . 129 130 . 138 143 3.1 Theory: Static Bayesian Games and Bayesian Nash Equilibrium . . . . . . . . . . . . . . . . . . . . . 144 3.1.A An Example: Cournot Competition under Asymmetric Information . . . . . . . . 3.1.B Normal-Form Representation of Static Bayesian Games . . . . . . . . . . . . . 3.1.C Definition of Bayesian Nash Equilibrium 3.2 Applications . . . . . 3.2.A Mixed Strategies Revisited 3.2.B An Auction . . . . . 3.2.C A Double Auction . The Revelation Principle Further Reading Problems References 3.3 3.4 3.5 3.6 II Dynamic Games of Incomplete Information Introduction to Perfect Bayesian Equilibrium. 4.1 4.2 Signaling Games . . . . . . . . . . . . . . 4.2.A Perfect Bayesian Equilibrium in Signaling .144 .146 .149 .152 152 .155 .158 164 .168 .169 .172 173 . 175 . 183 Games. . . . . . . . . . . . . . . . . . . .. .183
Contents 4.3 Job-Market Signaling 4.2.B . . . . . . . . . . . . . 4.2.C Corporate Investment and Capital Structure 4.2.0 Monetary Policy . . . . . . . . . Other Applications of Perfect Bayesian Equilibrium . . . . . . . . . . . . . 4.3.A Cheap-Talk Games. . . . . . . . 4.3.B Sequential Bargaining under Asymmetric Information. . . . . . . . . . . . 4.3.C Reputation in the Finitely Repeated Prisoners' Dilemma . . . . . . . . . 4.4 4.5 4.6 4.7 Refinements of Perfect Bayesian Equilibrium . Further Reading Problems References . Index ix .190 . 205 .208 .210 .210 .218 .224 .233 .244 .245 .253 257
Preface Game theory is the study of multiperson decision problems. Such problems arise frequently in economics. As is widely appreciated, for example, oligopolies present multiperson problems - each firm must consider what the others will do. But many other ap plications of game theory arise in fields of economics other than industrial organization. At the micro level, models of trading processes (such as bargaining and auction models) involve game theory. At an intermediate level of aggregation, labor and finan cial economics include game-theoretic models of the behavior of a firm in its input markets (rather than its output market, as in an oligopoly). There also are multiperson problems within a firm: many workers may vie for one promotion; several divisions may compete for the corporation's investment capital. Finally, at a high level of aggregation, international economics includes models in which countries compete (or collude) in choosing tariffs and other trade policies, and macroeconomics includes models in which the monetary authority and wage or price setters interact strategically to determine the effects of monetary policy. This book is designed to introduce game theory to those who will later construct (or at least consume) game-theoretic models in applied fields within economics. The exposition emphasizes the economic applications of the theory at least as much as the pure theory itself, for three reasons. First, the applications help teach the theory; formal arguments about abstract games also ap pear but playa lesser role. Second, the applications illustrate the process of model building - mal description of a multiperson decision situation into a formal, game-theoretic problem to be analyzed. Third, the variety of ap plications shows that similar issues arise in different areas of eco nomics, and that the same game-theoretic tools can be applied in the process of translating an infor
xii PREFACE each setting. In order to emphasize the broad potential scope 01 : the theory, conventional applications from industrial organization. largely have been replaced by applications from labor, macro, and other applied fields in economics. l We will discuss four classes of games: static games of com (A game has incomplete information if one plete information, dynamic games of complete information, static games of incomplete information, and dynamic games of incom plete information. player does not know another player's payoff, such as in an auc tion when one bidder does not know how much another bidder is willing to pay for the good being sold.) Corresponding to these four classes of games will be four notions of equilibrium in games: Nash equilibrium, subgame-perfect Nash equilibrium, Bayesian Nash equilibrium, and perfect Bayesian equilibrium. Two (related) ways to organize one's thinking about these equi librium concepts are as follows. First, one could construct se quences of equilibrium concepts of increasing strength, where stronger (Le., more restrictive) concepts are attempts to eliminate implausible equilibria allowed by weaker notions of equilibrium. We will see, for example, that subgame-perfect Nash equilibrium is stronger than Nash equilibrium and that perfect Bayesian equi librium in turn is stronger than sub game-perfect Nash equilib rium. Second, one could say that the equilibrium concept of in terest is always perfect Bayesian equilibrium (or perhaps an even stronger equilibrium concept), but that it is equivalent to Nash equilibrium in static games of complete information, equivalent to subgame-perfection in dynamic games of complete (and per fect) information, and equivalent to Bayesian Nash equilibrium in static games of incomplete information. The book can be used in two ways. For first-year graduate stu dents in economics, many of the applications will already be famil iar, so the game theory can be covered in a half-semester course, leaving many of the applications to be studied outside of class. For undergraduates, a full-semester course can present the theory a bit more slowly, as well as cover virtually all the applications in class. The main mathematical prerequisite is single-variable cal culus; the rudiments of probability and analysis are introduced as needed. 1 A good source for applications of game theory in industrial organization is Tirole's The Theory of Industrial Organization (MIT Press, 1988).
Preface xiii I learned game theory from David Kreps, John Roberts, and Bob Wilson in graduate school, and from Adam Brandenburger, Drew Fudenberg, and Jean Tirole afterward. lowe the theoreti cal perspective in this book to them. The focus on applications and other aspects of the pedagogical style, however, are largely due to the students in the MIT Economics Department from 1985 to 1990, who inspired and rewarded the courses that led to this book. I am very grateful for the insights and encouragement all these friends have provided, as well as for the many helpful com ments on the manuscript I received from Joe Farrell, Milt Harris, George Mailath, Matthew Rabin, Andy Weiss, and several anony mous reviewers. Finally, I am glad to acknowledge the advice and encouragement of Jack Repcheck of Princeton University Press and finandal support from an Olin Fellowship in Economics at the Na tional Bureau of Economic Research.
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