First Author:   Gilles Dufrenot University of Aix-Marseille, DEFI, and CEPII lopaduf@aol.com   Chateau La Farge, Route des Milles Les Milles, 13290, France       Second Author: Valerie Mignon University of Paris Ouest, EconomiX-CNRS and CEPII valerie.mignon@u-paris10.fr   Nanterre, 92001, France       Third Author: Anne Peguin-Feissolle GREQAM-CNRS anne.peguin@univmed.fr   Centre de la Charite, 2 rue de la Charite Marseille, 13236, France