Neri Salvadori Department of Economics, University of Pisa   Via Cosimo Ridolfi, 10 Pisa, Tuscany/PI I - 56124 Italy   cicse-lecture@ec.unipi.it   http://www.dse.ec.unipi.it/persone/docenti/salvadori_neri.asp           JEL Areas: O4 : Economic Growth and Aggregate Productivity: General J : Labor and Demographic Economics