Wissem Khanfir University of Sfax   road of teniour kilometer 5 Avenue Hbib Khanfir sfax, sfax 3041 Tunisia   khanfirwissemfseg@yahoo.fr             JEL Areas: E2 : Macroeconomics: Consumption, Saving, Production, Employment, and Investment: General (includes Measurement and Data) C2 : Single Equation Models; Single Variables: General