"Efficient Sequential Screening"A seller of an item faces a potential buyer whose valuation depends on multiple private signals. When there are informational externalities and the buyer's private signals arrive all at once efficient implementation is impossible. We show that if the buyer's private signals arrive over time then the seller can implement efficiency even in the presence of informational externalities.
"Cheap Talk in Allocation Problems" - joint with Ran WekslerWe consider a partially informed principal who needs to allocate a single good among multiple agents. Each agent wants to receive the good and holds partial information about the principal’s payoff from allocating the object to him. Both the agents’ and the principal’s signals are ordered in the first-order stochastic dominance sense. We show that effective information may be transmitted from the agents to the principal via cheap-talk communication despite the fact that each agent always prefers to receive the good. We characterize the information structures that support effective information transmission, and analyze how information transmission considerations affect the optimal signal function of the principal.
"Ex-Post Implementation with Social Preferences"The current literature on mechanism design in models with social preferences discusses social-preference-robust mechanisms, i.e., mechanisms that are implementable in any environment with social preferences. The literature also discusses payoff-information-robust mechanisms, i.e., mechanisms that are implementable for any belief and higher-order beliefs of the agents about the payoff types of the other agents. In the present paper we address the question of whether deterministic mechanisms that are robust in both of these dimensions exist. We consider environments where each agent holds private information about his personal payoff and about the existence and extent of his social preferences. In such environments a mechanism is robust in both dimensions only if it is ex-post implementable, i.e., only if incentive compatibility holds for every realization of payoff signals and for every realization of social preferences. We show that ex-post implementation of deterministic mechanisms is impossible in such environments; i.e., deterministic mechanisms that are both social-preference-robust and payoff-information-robust do not exist.
"Implementation in Models of Independent, Private, and Multivariate Values"We consider the problem of implementation in models of independent private values in which the valuation an agent attributes to a particular alternative is a function from a multidimensional Euclidean space to the real line. We first consider implementation by standard mechanisms, that include a decision rule and a profile of personal transfers. We present impossibility results on the implementation of decision rules that assign different outcomes to profiles of signals that result in the same profile of valuations. We then consider implementation by extended mechanisms that include, in addition to a decision rule and a profile of personal transfers, a profile of functions that affect the arguments of the valuation functions. We show that decision rules that assign different outcomes to profiles of signals that result in the same profile of valuations can be implemented by such mechanisms.