First Author:   ben mbarek hassene ESSEC business school of Tunisia hassene_mbarek@yahoo.fr   tunis, 1013, Tunisie   +21624946948(Phone) +21624946948(Fax) Second Author: Ben mbarek kais ENSI university of manouba, Tunisia kaisfsegt@yahoo.fr   tunis, 1013, Tunisie   +21624946948(Phone)