1. Department of Public Health, Institute of Tropical Medicine, Nationalestraat 155, 2000 Antwerp, Belgium
2. Netherlands Institute for Health Services Research (NIVEL), Otterstraat 118-124, 3513 CR Utrecht, The Netherlands
3. Department of General Practice and Elderly Care Medicine, EMGO Institute for Health and Care Research VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands