First Author:   FTITI ZIED Hight Business institute of Tunsia ISG- FIESTA laboratory and UAQUAP Laboratory zftitio@gmail.com   zftitio@gmail.com , 69120, France   0033(6)48177214(Phone) 0033(6)48177214(Fax) http://ideas.repec.org/e/pft1.html Second Author: Sahbi Saadi Hight Business institute of Tunsia ISG and UAQUAP Laboratory essaadi_s@yahoo.fr   , Tunisia   0021698604105(Phone)   http://ideas.repec.org/e/pes65.html