1 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; Gastroenterology Unit, Department of Gastroenterology, Dermatovenerology and Rheumatology, Karolinska University Hospital, Stockholm, Sweden.
2 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
3 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; Department of Paediatrics, Örebro University Hospital, Örebro, Sweden; Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York.