Akim Al-mouksit CRES (Consortium for Economic and Social Research), Dakar, Senegal   Cité Iba Ndiaye Diadji, n° 1 & 2, Pyrotechnie Dakar, C.P: 12023 Senegal   akim@cres-sn.org   http://www.cres-sn.org           JEL Areas: C1 : Econometric and Statistical Methods: General C4 : Econometric and Statistical Methods: Special Topics