1. Northern Centre for Healthcare Research, Department of Public Health and Health Psychology; University Medical Centre; Groningen PO Box 196, 9700 AD Groningen The Netherlands
2. Health Care Studies, Section of Medical Sociology; Maastricht University; PO Box 616, 6200 MD Maastricht The Netherlands
3. Behavioral Sciences; University of Pennsylvania; Philadelphia USA
4. Department of Cardiology; University Medical Centre, Groningen; PO Box 30.001, 9700 RB Groningen The Netherlands