1. Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden;
2. Division of Clinical Epidemiology, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden;
3. Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden;
4. Department of Pediatric Gastroenterology and Nutrition, Sachs' Children and Youth Hospital, Stockholm, Sweden;
5. Department of Internal Medicine, Sahlgrenska University Hospital, Gothenburg, Sweden;
6. Department of Pediatrics, Orebro University Hospital, Orebro, Sweden;
7. Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York, USA.