Francois Gardes Paris School of Economics, University Paris 1 Pathéon Sorbonne   106-112 Bd. de l'Hôpital, Paris, 75013 France   gardes@univ-paris1.fr             JEL Areas: E3 : Prices, Business Fluctuations, and Cycles: General (includes Measurement and Data) D1 : Household Behavior: General