[1] Univ Milano Bicocca, Dept Stat & Quantitat Methods, Via Bicocca Degli Arcimboldi 8, I-20126 Milan, Italy
[2] Univ Svizzera Italiana, Fac Econ, Lugano, Switzerland
[3] Univ Oxford, Dept Stat, Oxford, England
[4] Univ Oxford, Nuffield Coll, Oxford, England
[5] Univ Groningen, Dept Sociol, Groningen, Netherlands