1 Medical University of Geneva, 1208 Geneva, Switzerland. Electronic address: jean-pierre.michel@unige.ch.
2 Neurology, Public Health, Disability Unit and Coma Research Centre, Fondazione IRCCS Instituto Neurologico Carlo Besta, Milan, Italy.
3 Gerontology Center, University of Zurich, Zurich, Switzerland.
4 Social Epidemiology Research Group, Department of Health Service and Population Research, Institute of Psychiatry, Psychology, and Neuroscience, King's College London, London, UK.