Rodolphe Dos santos ferreira BETA, University of Strasbourg   BETA 61 avenue de la Forêt Noire Strasbourg, 67085 France   rdsf@unistra.fr   http://www.beta-umr7522.fr/-DOS-SANTOS-FERREIRA-Rodolphe           JEL Areas: D4 : Market Structure and Pricing: General E3 : Prices, Business Fluctuations, and Cycles: General (includes Measurement and Data)