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Much of the literature on mechanism design and implementation uses the revelation principle to restrict attention to direct mechanisms. This is without loss of generality in a well defined sense. It is, however, restrictive if one is concerned with the set of equilibria, if one is concerned about the size of messages that will be sent, or if one is concerned about privacy. We showed in McLean and Postlewaite (2014) that when agents are informationally small, there exist small modifications to VCG mechanisms in interdependent value problems that restore incentive compatibility. We show here how one can construct a two-stage mechanism that similarly restores incentive compatibility while improving upon the direct one stage mechanism in terms of privacy and the size of messages that must be sent. The first stage essentially elicits that part of the agents' private information that induces interdependence and reveals it to all agents, transforming the interdependent value problem into a private value problem. The second stage is a VCG mechanism for the now private value problem. Agents typically need to transmit substantially less information in the two stage mechanism than would be necessary for a single stage mechanism. Lastly, the first stage that elicits the part of the agents' private information that induces interdependence can be used to transform certain other interdependent value problems into private value problems. Download Paper
We showed in McLean and Postlewaite (2014) that when agents are informationally small, there exist small modifications to VCG mechanisms in interdependent value problems that restore incentive compatibility. This paper presents a two-stage mechanism that similarly restores incentive compatibility. The first stage essentially elicits that part of the agents’ private information that induces interdependence and reveals it to all agents, transforming the interdependent value problem into a private value problem. The second stage is a VCG mechanism for the now private value problem. Agents typically need to transmit substantially less information in the two stage mechanism than would be necessary for a single stage mechanism. Lastly, the firrst stage that elicits the part of the agents’ private information that induces interdependence can be used to transform certain other interdependent value problems into private value problems. Download Paper
It is well-known that the ability of the Vickrey-Clarke-Groves (VCG) mechanism to implement efficient outcomes for private value choice problems does not extend to interdependent value problems. When an agent’s type affects other agents’ utilities, it may not be incentive compatible for him to truthfully reveal his type when faced with CGV payments. We show that when agents are informationally small, there exist small modifications to CGV that restore incentive compatibility. We further show that truthful revelation is an approximate ex post equilibrium. Lastly, we show that in replicated settings aggregate payments sufficient to induce truthful revelation go to zero. Download Paper
We consider repeated games with private monitoring that are "close" to repeated games with public/perfect monitoring. A private monitoring information structure is close to a public monitoring information structure when private signals can generate approximately the same distribution of the public signal once they are aggregated into a public signal by some public coordination device. A player's informational size associated with the public coordination device is the key to inducing truth-telling in nearby private monitoring games when communication is possible. A player is informationally small given a public coordination device if she believes that her signal is likely to have a small impact on the public signal generated by the public coordinating device. We show that a uniformly strict equilibrium with public monitoring is robust in a certain sense: it remains an equilibrium in nearby private monitoring repeated games when the associated public coordination device, which makes private monitoring close to public monitoring, keeps every player informationally small at the same time. We also prove a new folk theorem for repeated games with private monitoring and communication by exploiting the connection between public monitoring games and private monitoring games via public coordination devices. Download Paper
It is well-known that the ability of the Vickrey-Clarke-Groves (VCG) mechanism to implement efficient outcomes for private value choice problems does not extend to interdependent value problems. When an agent’s type affects other agents’ utilities, it may not be incentive compatible for him to truthfully reveal his type when faced with CGV payments. We show that when agents are informationally small, there exist small modifications to CGV that restore incentive compatibility. We further show that truthful revelation is an approximate ex post equilibrium. Lastly, we show that in replicated settings aggregate payments sufficient to induce truthful revelation go to zero. Download Paper
For repeated games with noisy private monitoring and communication, we examine robustness of perfect public equilibrium/subgame perfect equilibrium when private monitoring is close to some public monitoring. Private monitoring is close. to public monitoring if the private signals can generate approximately the same public signal once they are aggregated. Two key notions on private monitoring are introduced: Informational Smallness and Distributional Variability. A player is informationally small if she believes that her signal is likely to have a small impact when private signals are aggregated to generate ate a public signal. Distributional variability measures the variation in a player's conditional beliefs over the generated public signal as her private signal varies. When informational size is small relative to distributional variability (and private signals are sufficiently close to public monitoring), a uniformly strict equilibrium with public monitoring remains an equilibrium with private monitoring and communication. To demonstrate that uniform strictness is not overly restrictive, we prove a uniform folk theorem with public monitoring which, combined with our robustness result, yields a new folk theorem for repeated games with private monitoring and communication. Download Paper
Conflicts of interest arise between a decision maker and agents who have information pertinent to the problem because of differences in their preferences over outcomes. We show how the decision maker can extract the information by distorting the decisions that will be taken, and show that only slight distortions will be necessary when agents are informationally small. We further show that as the number of informed agents becomes large the necessary distortion goes to zero. We argue that the particular mechanisms analyzed are substantially less demanding informationally than those typically employed in implementation and virtual implementation. In particular, the equilibria we analyze are conditionally dominant strategy in a precise sense. Further, the mechanisms are immune to manipulation by small groups of agents. Download Paper
It is understood that rational expectations equilibria may not be incentive compatible: agents with private information may be able to affect prices through the information conveyed by their market behavior. We present a simple general equilibrium model to illustrate the connection between the notion of informational size presented in McLean and Postlewaite (2002) and the incentive properties of market equilibria. Specifically, we show that fully revealing market equilibria are not incentive compatible for an economy with few privately informed producers because of the producers' informational size, but that replicating the economy decreases agents' informational size. For sufficently large economies, there exists an incentive compatible fully revealing market equilibrium. Download Paper
We analyze the ex ante incentive compatible core for replicated private information economies. We show that any allocation in the core when the economy is replicated sufficiently often is approximately Walrasian for the associated Arrow-Debreu economy. Download Paper
We develop an auction model for the case of interdependent values and multidimensional signals in which agents' signals are correlated. We provide conditions under which a modification of the Vickrey auction which includes payments to the bidders will result in an ex post efficient outcome. Furthermore, we provide a definition of informational size such that the necessary payments to bidders will be arbitrarily small if agents are sufficiently informationally small. Download Paper
In McLean and Postlewaite (2002), we analyzed pure exchange economies with asymetrically informed agents. We defined a notion of informational size and showed that, when the aggregate information of all agents resolves nearly all the uncertainty regarding the state of nature, the conflict between incentive compatibility and (ex post) efficiency can be made small if agents have sufficiently small informational size. This paper investigates the relationship between informational size and efficiency for the case in which nontrivial aggregate uncertainty is present, i.e., when significant uncertainty about the world persists even when the information of all agents is known. We prove the existence of incentive compatible, individually rational and nearly ex post efficient allocations without assuming negligible aggregate uncertainty when agents have small informational size relative to informational variability. We further show that the conflict between incentive compatibility and efficiency asymptotically vanishes when an economy is replicated. Download Paper
We develop an auction model for the case of interdependent values and multidimensional signals in which agents' signals are correlated. We provide conditions under which a modification of the Vickrey auction which includes payments to the bidders will result in an ex post efficient outcome. Furthermore, we provide a definition of informational size such that the necessary payments to bidders will be arbitrarily small if agents are sufficiently informationally small. Download Paper
In McLean and Postlewaite (2001), we analyzed a general equilibrium model with asymmetrically informed agents. We presented a notion of informational size and showed (among other things) that when agents' information as a whole resolved nearly all the uncertainty, the conflict between incentive compatibility and (ex post) efficiency can be made arbitrarily small if agents are sufficiently small informationally. This paper extends the analysis of the relationship between informational size and efficiency to the case in which there is nontrivial aggregate uncertainty, that is, when there is significant uncertainty about the world even when the information of all agents is known. We further show that the conflict between incentive compatibility and efficiency asymptotically vanishes when an economy is replicated. Download Paper
We develop an auction model for the case of interdependent values and multidimensional signals in which agents' information is not independent. We show that a modification of the Vickrey auction which includes payments to the bidders will result in an efficient outcome under very good general conditions. Further, we provide a definition of informational size such that the necessary payments to bidders will be arbitrarily small if agents are sufficiently informationally small. Download Paper
We examine a general equilibrium model with asymetrically informed agents. The presence of asymmetric information generally presents a conflict between incentive compatibility and Pareto efficiency. We present a notion of informational size and show that the conflict between incentive compatibility and efficiency can be made arbitrarily small if agents are sufficiently small informationally. Download Paper
We examine the ex ante incentive compatible core, and show that generically, when agents are informationally small in the sense of McLean and Postlewaite (1999), the ex ante incentive compatible core is nonempty. Download Paper