1. Epidemiologist, Maastricht University, Department of General Practice, School for Public Health and Primary Care (CAPHRI), PO Box 616, 6200 MD Maastricht, The Netherlands.
2. Health Scientist, University Hospital Maastricht, Department of Paediatrics, Maastricht, The Netherlands.
3. Paediatric Pulmonologist, University Hospital Maastricht, Department of Paediatrics, Maastricht, The Netherlands.
4. Professor of Preventive Medicine, Maastricht University, Department of General Practice, School for Public Health and Primary Care (CAPHRI), Maastricht, The Netherlands.