[1] Minist Econ & Finanze, Dipartimento Finanze, Direz Studi & Ric Econ Fiscali, Via Normanni 5, I-00184 Rome, Italy
[2] Univ Piemonte Orientale, Dept Econ & Business Studies, Via Ettore Perrone 18, I-28100 Novara, Italy
[3] CeRP Collegio Carlo Alberto, Piazza Vincenzo Arbarello 8, I-10122 Turin, Italy
[4] Univ Milan, Dept Econ Management & Quantitat Methods, Via Conservatorio 7, I-20122 Milan, Italy