The Relevance of Private Information in Mechanism Design

A number of recent results in mechanism design literature show that in virutally all mechanism design environments of interest, as long as agents' private information is correlated. It is possible to design mechanisms that leave agents with arbitrarily small information rents. Thus, while agents may possess exclusive private information, it is irrelevant for the purpose of normative economic analysis, since it is still always possible to implement any outcome as if the agent's private information was commonly known. This paper presents a critique of these results.