First Author:   Thabet Khaled Higher School of Economic and Commercial Sciences of Tunis, Tunisia khthabet@yahoo.com   khthabet@yahoo.com Bardo, 2000, TUNISIA   (+216) 54 439 436(Phone) (+216) 54 439 436(Fax) Second Author: Karima Ben Slimane Higher Institute of Management of Bizerte (ISG BIZERTE) karimabsg@yahoo.fr   karimabsg@yahoo.fr   (+216) 99 570 636(Phone)