Montassar Riahi Univ. Manouba, ESCT, LARIMRAF LR21ES29, Tunisia ; Université de Poitiers, CEREGE, UR 13564, France   , Tunisia   montassar.riahi1@hotmail.com             JEL Areas: G1 : General Financial Markets: General (includes Measurement and Data) C5 : Econometric Modeling: General