微觀經(jīng)濟(jì)學(xué)（趙耀輝）第28章-文庫吧
2025-04-24 17:01 本頁面
【正文】 Dilemma （ 囚徒困境） . The Prisoner’s Dilemma What plays are we likely to see for this game? Clyde Bonnie (5,5) (30,1) (1,30) (10,10) S C S C The Prisoner’s Dilemma If Bonnie plays Silence then Clyde’s best reply is Confess. Clyde Bonnie (5,5) (30,1) (1,30) (10,10) S C S C The Prisoner’s Dilemma If Bonnie plays Silence then Clyde’s best reply is Confess. If Bonnie plays Confess then Clyde’s best reply is Confess. Clyde Bonnie (5,5) (30,1) (1,30) (10,10) S C S C The Prisoner’s Dilemma So no matter what Bonnie plays, Clyde’s best reply is always Confess. Confess is a dominant strategy for Clyde. Clyde Bonnie (5,5) (30,1) (1,30) (10,10) S C S C The Prisoner’s Dilemma Similarly, no matter what Clyde plays, Bonnie’s best reply is always Confess. Confess is a dominant strategy for Bonnie also. Clyde Bonnie (5,5) (30,1) (1,30) (10,10) S C S C The Prisoner’s Dilemma So the only Nash equilibrium for this game is (C,C), even though (S,S) gives both Bonnie and Clyde better payoffs. The only Nash equilibrium is inefficient. Clyde Bonnie (5,5) (30,1) (1,30) (10,10) S C S C Other Examples of Prisoner’s Dilemma ?Cheating in a Cartel. ?Price petition. ?Military petition in the cold war. How to Avoid Prisoner’s Dilemma ? Repeated games – Finite number of periods – Infinite number of periods or uncertain about the (finite number of periods) ?Titfortat ?The demand factor (water meters and airlines) ? Binding contract Multiple Equilibria Chicken game Youth 2 Youth 1 Swerve Straight Swerve (0,0) (1,1) (1,1) (2,2) Straight Multiple Equilibria ?Sometimes a game has more than one Nash equilibrium and it is hard to say which is more likely to occur. ?Solutions: –Coordination –Strategic behavior。 establish reputation –Sequential moves Sequential Game ?When such a game is sequential it is sometimes possible to argue that one of the Nash equilibria is more likely to occur than the other. Who Plays When? ?When players chose their strategies simultaneously, a game is a simultaneous play game. ?But there are games in which one player plays before another player. ?Such games are sequential play games. ?The player who plays first is the leader. The player who plays second is the follower. A Sequential Game Example Player B Player A (U,L) and (D,R) are both Nash equilibria when this game is played simultaneously and we have no way of deciding which equilibrium is more likely to occur. L R U D (3,9) (0,0) (1,8) (2,1) A Sequential Game Example Player B Player A Suppose instead that the game is played sequentially, with A leading and B following. We can rewrite the game in its extensive form. L R U D (3,9) (0,0) (1,8) (2,1) A Sequential Game Example U D L L R R (3,9) (1,8) (0,0) (2,1) A B B A plays first. B plays second. A Sequential Game Example U D L L R R (3,9) (1,8) (0,0) (2,1) A B B A plays first. B plays second. (U,L) is a Nash equilibrium. A Sequential Game Example U D L L R R (3,9) (1,8) (0,0) (2,1) A B B A plays first. B
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