Econ 357 ASSIGNMENT 3
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ASSIGNMENT 3 (Econ 357)
Problem 1:
Consider the following simultaneous move game with two players, denoted by 1 and 2:
1. Is there a strategy for any of the players which a player would never choose?
Solution: R is strictly dominated by M and therefore it is never chosen as a best response by player 2.
2. If there is a strategy which a player never chooses (it is called, a dominated strategy), and this fact is known among the players, find the equilibria of the game.
Hint: In a mixed strategy equilibrium, think about how probabilities should be assigned if there exists a strategy which a player never chooses.
Solution: There is no pure strategy equilibrium in this game. To find a Nash equilibrium in mixed strategies notice that player 1 assigns probabil- ity 0 to player 2 choosing R as it is a strictly dominated strategy. Assign probabilities p and q to the strategies T and L. If 1 plays T then his expected payoff is q, and if 1 plays B then his expected payoff is 2(1 − q). The probability q which makes him indifferent between choosing T and B - and therefore allows him to randomize - solves q = 2(1 − q) such that q = . For player 2, the expected payoffs from playing L and M are respectively 2(1 − p) and 1, where p = makes the player 2 indifferent between choosing L and M . Hence, the mixed strategy equilibrium is (p = , q = ).
Problem 2:
Consider the following game: there are two players, an incumbent (denoted I) and a potential entrant (denoted E) to the market. The entrant has two actions: it can either enter the market in which the incumbent operates, or not enter. The incumbent has two actions: it can either fight the entrant, or accommodate. The payoffs are as follows: if E enters and I fights, E gets -1 and I gets 2. If E does not enter, I gets 10 for any of its two actions, and E gets 0. If E enters and I accommodates, then both get the payoff 5.
1. Suppose that both players act simultaneously. Depict the game. Find the Nash equilibria (in pure strategies).
Solution: The equilibria are highlighted by a circle:
2. Now suppose that E moves first, and then the I follows. Depict this sequential game with the help of a game tree. What is the equilibrium of the game? (remember from the lecture that we have to apply ”backward
reasoning” - start from the end and move to the start of the game).
Solution: The equilibrium is highlighted by red arrows:
3. Suppose that before the game starts, I announces: ”If E enters, than I always fight”. Does it convince E in a simultaneous move game? Does it convince E in the sequential game? Why?
Solution: In a simultaneous move game there is an equilibrium in which I fights and E does not enter. However, the threat to fight the E is not
credible in a sequential move game: notice that the sequential game has only one equilibrium in which E enters and I accommodates. This is because - conditional on entry - it is not rational for I to fight. Therefore, conditional on entry, I accommodates.
2022-04-26