Fernando Bruna Universidade da Coruña, Department of Economics   Facultade de Economía e Empresa, Campus de Elvinna A Corunna, A Corunna 15071 Spain   f.bruna@udc.es   http://pdi.udc.es/en/File/Pdi/9Z97J           JEL Areas: O4 : Economic Growth and Aggregate Productivity: General C1 : Econometric and Statistical Methods: General