Information Acquisition and Efficient Mechanism Design

We consider a general mechanism design setting where each agent can acquire (covert) information before participating in the mechanism. The central question is whether a mechanism exists which provides the efficient incentives for information ac-quisition ex ante and implements the efficient allocation conditional on the private information ex post. It is shown that in every private value environment the Vickrey-Clark-Groves mech-anism guarantees both ex ante as well as ex post efficiency. In contrast, with common values, ex ante and ex post efficiency cannot be reconciled in general. Sufficient con-ditions in terms of sub- and supermodularity are provided when (all) ex post efficient mechanisms lead to private under- or overacquisition of information