[1] NW London Hosp Trust, St Marks Hosp, Canc Res UK Colorectal Canc Unit, Harrow HA1 3UJ, Middx, England
[2] Univ Oxford, Canc Epidemiol Unit, Oxford OX1 2JD, England
[3] NHS Canc Screening Programmes, Sheffield, S Yorkshire, England
[4] UCL, Dept Clin Hlth Psychol, London WC1E 6BT, England
[5] Ctr Dis Control & Prevent, Div Canc Prevent & Control, Atlanta, GA USA
[6] Amer Canc Soc, Canc Control Dept, Atlanta, GA 30329 USA