1. Institute of Health and Society; University of Oslo; Oslo Norway
2. Primary Care Research Unit; Vårdcentralen Värmlands Nysäter; Värmland Sweden
3. Department of Transplantation Medicine; K. G. Jebsen Center for Colorectal Cancer Research; Oslo University Hospital; Oslo Norway
4. Department of Epidemiology; Harvard T.H. Chan School of Public Health; Boston MA USA
5. Department of Medicine; Sørlandet Hospital; Kristiansand Norway
6. Division of Preventive Medicine; Brigham and Women's Hospital; Harvard Medical School; Boston MA USA
7. Department of Medical Epidemiology and Biostatistics; Karolinska Institutet; Stockholm Sweden
8. Telemark Hospital; Skien Norway