1. Cancer Research UK Health Behaviour Unit, Department of Epidemiology and Public Health, University College London, London WC1E 6BT, UK
2. Wolfson Endoscopy Unit, St Mark's Hospital, Harrow, Middlesex HA1 3UJ, UK
3. Cancer Research UK Centre for Epidemiology, Mathematics and Statistics, Wolfson Institute of Preventive Medicine, Charterhouse Square, London, UK
4. Department of Epidemiology and Public Health, UCL
5. Cancer Research UK Health Behaviour Unit, Department of Epidemiology & Public Health, UCL
6. Cancer Research UK Colorectal Cancer Unit, St. Mark's Hospital, Harrow, Middlesex H41 3UJ, UK