1 Clinical Effectiveness Research Group, Institute of Health and Society, University of Oslo, Postbox 1089, 0318, Blindern, Oslo, Norway. magnus.loberg@medisin.uio.no.
2 Department of Transplantation Medicine and KG Jebsen Colorectal Cancer Research Center, Oslo University Hospital, Oslo, Norway. magnus.loberg@medisin.uio.no.
3 Clinical Effectiveness Research Group, Institute of Health and Society, University of Oslo, Postbox 1089, 0318, Blindern, Oslo, Norway.
4 Department of Transplantation Medicine and KG Jebsen Colorectal Cancer Research Center, Oslo University Hospital, Oslo, Norway.
5 Department of Epidemiology, Harvard TH Chan School of Public Health, Boston, MA, USA.