1. Department of Gastroenterology; Faculty of Medicine and Health; Örebro University; Örebro Sweden
2. Clinical Epidemiology and Biostatistics; School of Medical Sciences; Örebro University; Örebro Sweden
3. Clinical Epidemiology Unit; Department of Medicine; Karolinska Institutet; Stockholm Sweden
4. Department of Epidemiology and Public Health; University College London; London UK