1. Department of Cardiology; University Medical Center Groningen (UMCG), University of Groningen; PO Box 30.001 9700 RB Groningen The Netherlands
2. Department of Social- and Welfare Studies, Department of Health Sciences; University of Linköping; Norrköping Sweden
3. Department of Health Sciences; University Medical Center Groningen (UMCG), University of Groningen; The Netherlands
4. Department of Epidemiology; University Medical Center Groningen (UMCG), University of Groningen; The Netherlands