aCentre for Public Health, Queen's University Belfast, Belfast, Northern Ireland, UK

bCenter for Clinical Management Research, Ann Arbor Veterans Affairs Medical Center

cDivision of Gastroenterology, Department of Internal Medicine, University of Michigan Medical School

dRogel Cancer Center, University of Michigan, Ann Arbor, Michigan, USA

Correspondence to Andrew T. Kunzmann, Queen's University Belfast Faculty of Medicine Health and Life Sciences, Centre for Public Health, Institute of Clinical Sciences, Royal Victoria Hospital, Belfast, UK, BT12 6BA. E-mail: [email protected]