Ex Post Regret and the Decentralized Sharing of Information

Abstract

Firms reveal private information about the value of investment through their investment decisions. As a consequence they may have ex post regret once they see other firms' investments. We define a notion of rational expectations equilibrium for games which imposes a "no-regret" property. In this equilibrium, all firms make the same investment decision, but despite the absence of ex post regret, the investment herd can be inefficient. In addition equilibrium might not exist. We introduce a notion of probabilistic existence, and identify conditions under which, if the number of firms is large, enough information comes out so that investment herds are first-best efficient with high probability, and equilibrium exists with high probability.Journal of Economic LiteratureClassification Numbers: C7, D8. © 1999 Academic Press.