1. Department of General and Pediatric Surgery, Oslo University Hospital, Oslo, Norway
2. Department of Medicine, Norwegian University of Science and Technology, Trondheim, Trøndelag, Norway
3. Department of Biostatistics and Epidemiology, Oslo University Hospital, Oslo, Norway
4. Depratment of Clinical Medicine, University of Oslo Faculty of Medicine, Oslo, Norway
5. Department of Pediatric Surgery, St. Olavs Hospital Trondheim University Hospital, Trondheim, Trøndelag, Norway