1. University of Groningen University Medical Centre Groningen Department of General Practice and Elderly Care medicine FA21 PO Box 196 9700AD Groningen The Netherlands
2. Profundum Institute, Education and Research van Godewijckstraat 104a 3311 GX Dordrecht The Netherlands
3. University of Groningen University Medical Centre Groningen Department of Epidemiology FA21 PO Box 196 9700AD Groningen The Netherlands