1. Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway
2. Department of Pediatrics, Haukeland University Hospital, Bergen, Norway
3. Section of Epidemiology, Department of Public Health, University of Copenhagen, Copenhagen, Denmark
4. Epidemiology Branch, National Institute of Environmental Health Sciences, Durham, NC, USA
5. Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway
6. Department of Paediatrics and Adolescent Medicine, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark
7. Department of Health Promotion, Norwegian Institute of Public Health, Oslo, Norway
8. Norwegian Quality Improvement of Laboratory Examinations (Noklus), Haraldsplass Deaconess Hospital, Bergen, Norway