1 Leverhulme Centre for Demographic Science, Nuffield Department of Population Health, University of Oxford and Nuffield College, Oxford, UK.
2 Institute of Physical Science, University of Iceland, Reykjavik, Iceland.
3 Faculty of Medicine, University of Iceland, Reykjavik, Iceland.
4 Leverhulme Centre for Demographic Science, Nuffield Department of Population Health, University of Oxford and Nuffield College, Oxford, UK. melinda.mills@demography.ox.ac.uk.
5 Department of Genetics, University Medical Centre Groningen, Groningen, the Netherlands. melinda.mills@demography.ox.ac.uk.
6 Department of Economics, Econometrics and Finance, University of Groningen, Groningen, the Netherlands. melinda.mills@demography.ox.ac.uk.