1. Department of Applied Economics (Mathematics) Universidad de Málaga C/Ejido, 6 Malaga 29071 Spain
2. Polytechnic Institute of Coimbra ISCAC Business School Quinta Agrícola, Bencanta Coimbra 3040‐316 Portugal
3. INESC Coimbra – DEEC University of Coimbra Polo 2 Coimbra 3030‐290 Portugal
4. Department of Applied Economics (Statistics and Econometrics) Universidad de Málaga C/Ejido, 6 Malaga 29071 Spain