1. Health Inspectorate; The Hague The Netherlands
2. Department of Clinical Epidemiology; Biostatistics and Bioinformatics; Academic Medical Center; Amsterdam The Netherlands
3. Pediatric Respiratory Medicine and Allergy; Emma Children's Hospital; Academic Medical Center; Amsterdam The Netherlands
4. Department of General Practice; Academic Medical Center; Amsterdam The Netherlands
5. Department of General Practice; Erasmus Medical Center; Rotterdam The Netherlands