This paper investigates the Harsanyi-purifiability of mixed strategies in the repeated prisoners’ dilemma with perfect monitoring. We perturb the game so that in each period, a player receives a private payoff shock which is independently and identically distributed across players and periods. We focus on the purifiability of a class of one-period memory mixed strategy equilibria used by Ely and Välimäki in their study of the repeated prisoners’ dilemma with private monitoring. We find that the strategy profile is purifiable by perturbed-game finite-memory strategies if and only if it is strongly symmetric, in the sense that after every history, both players play the same mixed action. Thus “most” strategy profiles are not purifiable by finite memory strategies. However, if we allow infinite memory strategies in the perturbed game, then any completely-mixed equilibrium is purifiable.
Traders with short horizons and privately known trading limits interact in a market for a risky asset. Risk-averse, long horizon traders supply a downward sloping residual demand curve that face the short-horizon traders. When the price falls close to the trading limits of the short horizon traders, selling of the risky asset by any trader increases the incentives for others to sell. Sales become mutually reinforcing among the short term traders, and payoffs analogous to a bank run are generated. A “liquidity black hole” is the analogue of the run outcome in a bank run model. Short horizon traders sell because others sell. Using global game techniques, this paper solves for the unique trigger point at which the liquidity black hole comes into existence. Empirical implications include the sharp V-shaped pattern in prices around the time of the liquidity black hole.
Market participants’ risk attitudes, wealth and portfolio composition influence their positions in a pegged foreign currency and, therefore, may have important effects on the sustainability of currency pegs. We analyze such effects in a global game model of currency crises with continuous action choices. The model, solved in closed form, generates a rich set of theoretical predictions consistent with many popular and academic (unmodelled) speculations about the onset and timing of currency crises. The results extend linearly to a heterogeneous agent population.
Traders with short horizons and privately known trading limits interact in a market for a risky asset. Risk-averse, long horizon traders supply a downward sloping residual demand curve that face the short-horizon traders. When the price falls close to the trading limits of the short horizon traders, selling of the risky asset by any trader increases the incentives for others to sell. Sales become mutually reinforcing among the short term traders, and payoffs analogous to a bank run are generated. A “liquidity black hole” is the analogue of the run outcome in a bank run model. Short horizon traders sell because others sell. Using global game techniques, this paper solves for the unique trigger point at which the liquidity black hole comes into existence. Empirical implications include the sharp V-shaped pattern in prices around the time of the liquidity black hole.
We analyze the effect of risk aversion, wealth and portfolios on the behavior of investors in a global game model of currency crises with continuous action choices. The model generates a rich set of striking theoretical predictions. For example, risk aversion makes currency crises significantly less likely; increased wealth makes crises more likely; and foreign direct investment (illiquid investments in the target currency) make crises more likely. Our results extend linearly to a heterogeneous agent population.
The mechanism design literature assumes too much common knowledge of the environment among the players and planner. We relax this assumption by studying implementation on richer type spaces, with more higher order uncertainty.
We study the “ex post equivalence” question: when is interim implementation on all possible type spaces equivalent to requiring ex post implementation on the space of payoff types? We show that ex post equivalence holds when the social choice correspondence is a function and in simple quasi-linear environments. When ex post equivalence holds, we identify how large the type space must be to obtain the equivalence. We also show that ex post equivalence fails in general, including in quasi-linear environments with budget balance.
For quasi-linear environments, we provide an exact characterization of when interim implementation is possible in rich type spaces. In this environment, the planner can fully extract players’ belief types, so the incentive constraints reduce to conditions distinguishing types with the same beliefs about others’ types but different payoff types.
We consider parametric examples of two-bidder private value auctions in which each bidder observes her own private valuation as well as noisy signals about her opponent’s private valuation. In such multidimensional private value auction environments, we show that the revenue equivalence between the first and second price auctions breaks down and there is no definite revenue ranking; while the second price auction is always efficient allocatively, the first price auction may be inefficient and the inefficiency may increase as the signal becomes more informative; equilibria may fail to exist for the first price auction. We also show that auction mechanisms provide different incentives for bidders to acquire costly information about opponents’ valuation.
The mechanism design literature assumes too much common knowledge of the environment among the players and planner. We relax this assumption by studying implementation on richer type spaces.
We ask when ex post implementation is equivalent to interim (or Bayesian) implementation for all possible type spaces. The equivalence holds in the case of separable environments; examples of separable environments arise (1) when the planner is implementing a social choice function (not correspondence); and (2) in a quasilinear environment with no restrictions on transfers. The equivalence fails in general, including in some quasilinear environments with budget balance.
In private value environments, ex post implementation is equivalent to dominant strategies implementation. The private value versions of our results offer new insights into the relation between dominant strategy implementation and Bayesian implementation.
We consider parametric examples of two-bidder private value auctions in which each bidder observes her own private valuation as well as noisy signals about her opponent’s private valuation. In such multidimensional private value auction environments, we show that the revenue equivalence between the first and second price auctions breaks down and there is no definite revenue ranking; while the second price auction is always efficient allocatively, the first price auction may be inefficient and the inefficiency may increase as the signal becomes more informative; equilibria may fail to exist for the first price auction. We also show that auction mechanisms provide different incentives for bidders to acquire costly information about opponents’ valuation.
Keywords: Multidimensional auctions, Revenue equivalence, Allocative efficiency, Information acquisition
The mechanism design literature assumes too much common knowledge of the environment among the players and planner. We relax this assumption by studying implementation on richer type spaces, with more higher order uncertainty.
We study the “ex post equivalence” question: when is interim implementation on all possible type spaces equivalent to requiring ex post implementation on the space of payoff types? We show that ex post equivalence holds when the social choice correspondence is a function and in simple quasi-linear environments. When ex post equivalence holds, we identify how large the type space must be to obtain the equivalence. We also show that ex post equivalence fails in general, including in quasi-linear environments with budget balance.
For quasi-linear environments, we provide an exact characterization of when interim implementation is possible in rich type spaces. In this environment, the planner can fully extract players’ belief types, so the incentive constraints reduce to conditions distinguishing types with the same beliefs about others’ types but different payoff types.
Keywords: Mechanism design, Common knowledge, Universal type space, Interim equilibrium, Ex-post equilibrium, Dominant strategies
In a financial market where traders are risk averse and short lived, and prices are noisy, asset prices today depend on the average expectation today of tomorrow’s price. Thus (iterating this relationship) the date 1 price equals the date 1 average expectation of the date 2 average expectation of the date 3 price. This will not in general equal the date 1 average expectation of the date 3 price. We show how this failure of the law of iterated expectations for average belief can help understand the role of higher order beliefs in a fully rational asset pricing model and explain over-reaction to (noisy) public information.
One role of monetary policy is to coordinate expectations in the economy and greater transparency of monetary policy may lead to greater coordination. But if transparent monetary policy helps coordinate expectations, then it must also magnify mistakes.
One role of monetary policy is to coordinate expectations in the economy and greater transparency of monetary policy may lead to greater coordination. But if transparent monetary policy helps coordinate expectations, then it must also magnify mistakes.
JEL Classification: C7, E5
Keywords: Communication, monetary policy, transparency, common knowledge
In a financial market where traders are risk averse and short lived, and prices are noisy, asset prices today depend on the average expectation today of tomorrow’s price. Thus (iterating this relationship) the date 1 price equals the date 1 average expectation of the date 2 average expectation of the date 3 price. This will not in general equal the date 1 average expectation of the date 3 price. We show how this failure of the law of iterated expectations for average belief can help understand the role of higher order beliefs in a fully rational asset pricing model and explain over-reaction to (noisy) public information.