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