1. Department of Statistics, Sapienza University of Rome, Rome, Italy.
2. Department of Political Sciences, University of Roma Tre, Rome, Italy.
3. Italian National Institute of Statistics (ISTAT), Rome, Italy.
4. Interdisciplinary Centre on Population Change, University of Southern Denmark, Odense, Denmark.
5. Duke University Population Research Institute, Durham, NC, USA.
6. Department of Demography, University of California, Berkeley, CA, USA.