First Author:   Aymen Ben Rejeb Faculty of Economics and Management of Mahdia, University of Monastir and LAMIDED, Tunisia benredjeb_aymen@yahoo.fr   Sidi Messaoud Hiboun, 5111 Mahdia, Sidi Messaoud Hiboun, 5111 Mahdia , TUNISIA   +21697310188(Phone) +21697310188(Fax) Second Author: Taoufik Elkemali University of Montpellier – MRM, France and Faculty of Economics and Management of Mahdia, Tunisia elkemali@yahoo.fr