1. Department of Pedagogy, Psychology, Philosophy, University of Cagliari, 09123 Cagliari, Italy
2. Institute of Education, Faculty of Philosophy, Jagiellonian University, 31-007 Kraków, Poland
3. Unit of Statistics, IRCCS, Centro San Giovanni di Dio Fatebenefratelli of Brescia, 25125 Brescia, Italy
4. Department of Political and Social Sciences, University of Cagliari, 09123 Cagliari, Italy