1. Alterra, Green World Research, Department of Landscape and Spatial Planning, PO Box 47, 6700 AA Wageningen, The Netherlands
2. National Institute of Public Health and the Environment (RIVM), Postbus 1, 3720 BA Bilthoven, The Netherlands
3. Netherlands Institute for Health Services Research (NIVEL), Drieharingstraat 6, 3500 BN Utrecht, The Netherlands