1. Ecole des Hautes Etudes Commerciales (HEC), University of Montreal, 5255 Decelles Ave., Montreal, Quebec H3T 1V6, Canada
2. Center for Crisis Management, Graduate School of Business, University of Southern California, Los Angeles, CA 90089-1421, USA
3. Laboratoire d'Econometrie, Ecole Polytechnique, 1 rue Descartes, 75005 Paris, France