First Author:   wafa amor snoussi high institute of management wafa_snoussi@yahoo.fr   wafa_snoussi@yahoo.fr Ariana, 2080, Tunis   +21697981575(Phone) +21697981575(Fax) - Second Author: Mhamed-Ali El-Aroui university of management of Nabeul mhamed.elaroui@yahoo.com