Kaies Samet Dr. Faculty of Economic and Management Sciences of Sfax   Road of Gremda, km 0,5, Complex Medina Center, Block A, 1st stage Apartment 10 Sfax, Sfax 3027 Tunisia   Kaies.Samet@fsegs.rnu.tn             JEL Areas: C2 : Single Equation Models; Single Variables: General F4 : Macroeconomic Aspects of International Trade and Finance: General