Awatef Ourir FIESTA Laboratory, University of Tunis, High Business institute of Tunis (ISG), Tunisia.   25 Rue Kamel Attaturk 25 Rue Kamel Attaturk Bardo, Tunis 2000 Tunisie   ourirawatef@yahoo.fr             JEL Areas: G0 : Financial Economics: General C5 : Econometric Modeling: General