[1] Max Planck Inst Demog Res, D-18057 Rostock, Germany
[2] Duke Univ, Ctr Demog Studies, Durham, NC USA
[3] Duke Univ, Sanford Inst, Durham, NC USA
[4] Univ Calabria, Cell Biol Dept, Arcavacata Di Rende, Italy
[5] Univ Oxford, Phys & Theoret Chem Lab, Oxford OX1 2JD, England
[6] Univ Bologna, Dept Expt Pathol, I-40126 Bologna, Italy
[7] Univ So Denmark, Dept Stat & Demog, Copenhagen, Denmark