In the Netherlands, postal area code can be linked to aggregated data on income level, education and type of occupation of Dutch citizens (based on data from Statistics Netherlands) [1]. At the time of the trial, the Netherlands did not have a population-based colorectal cancer screening program. see more Invitees were

only allowed to undergo the allocated screening modality. Ethical approval was obtained before study initiation from the Dutch Health Council (2009/03WBO, The Hague, The Netherlands). The trial was registered in the Dutch trial register: NTR1829 (www.trialregister.nl). With the invitation, colonoscopy and CT colonography screening invitees received identically designed leaflets with information on colorectal cancer and colorectal cancer screening. These leaflets were derived from similar leaflets used in previous colorectal cancer screening

pilots. The information leaflet for colonoscopy invitees contained specific information on benefits and risks of colonoscopy, while the information leaflet of CT colonography invitees contained information on benefits and risks of CT colonography. Both leaflets contained information on follow-up in case of a positive test result (e.g. follow-up colonoscopy in case of a positive CT colonography result). Invitees who responded to the invitation were scheduled for a standardized consultation with a research fellow or research nurse to inform them about the bowel preparation and the procedure itself. In the CT colonography group all invitees were invited for a prior consultation by telephone, while in the colonoscopy group this website half of invitees were invited for a prior consultation at the outpatient clinic [28]. Data on differences between the two colonoscopy groups were recently published by Stoop et al. [29]. Responders were excluded from participation

when they had undergone a full colonic examination in the previous five years, when they had a life expectancy of less than 5 years, Carnitine palmitoyltransferase II or when they had been previously scheduled for surveillance colonoscopy because of a personal history of colorectal cancer, adenomatous polyps or inflammatory bowel disease. CT colonography responders were also excluded when they had been exposed to ionizing radiation for research purposes within the previous 12 months or when they had hyperthyroidism or iodine contrast allergy. All invitees received a questionnaire containing previously validated measures of knowledge and an attitude measure based on Marteau’s Multidimensional Measure of Informed Choice [18], [19], [30], [31] and [32]. Screenees received the questionnaire within 4 weeks before the screening procedure with the appointment confirmation, and were asked to return the questionnaire by mail or to bring the questionnaire to the hospital. All invitees who actively declined the invitation received the same questionnaire, as well as those invitees that did not respond within 4 weeks after the initial invitation (together with a reminder letter).