1. Department of Paediatrics Institute of Clinical Sciences, Sahlgrenska Academy Gothenburg Sweden
2. Department of Paediatrics Queen Silvia Children's Hospital Gothenburg Sweden
3. Statistiska konsultgruppen Gothenburg Sweden
4. Department of Paediatric Research University of Oslo and Oslo University Hospital Oslo Norway
5. Department of Medical Epidemiology and Biostatistics Karolinska Institutet Stockholm Sweden
6. Department of Paediatrics Örebro University Hospital Örebro Sweden
7. Department of Medicine Columbia University College of Physicians and Surgeons New York New York USA