Laurent Muller INRA, University of Grenoble-Alpes, UMR 1215 GAEL   BP 47 GRENOBLE Cedex 9, 38040 France   laurent.muller@grenoble.inra.fr   http://www.grenoble.inra.fr/           JEL Areas: C9 : Design of Experiments: General D1 : Household Behavior: General