[1] Univ Salerno, Dept Econ & Stat, Via Ponte Don Melillo, I-84084 Fisciano, SA, Italy
[2] Inst Univ Lisboa ISCTE IUL, Business Res Unit BRU IUL, Ava Forcas Armadas, P-1649026 Lisbon, Portugal
[3] Univ Salerno, CELPE, Ctr Econ Lavoro & Polit Econ, Fisciano, SA, Italy
[4] TU Wien, Inst Stat & Math Methods Econ, Wiedner Hauptstr 8-10, A-1040 Vienna, Austria