Selection process
Five districts (départements) were selected according to their characteristics and their CRC screening participation rates (< 30%): five different districts with a low participation rate were retained: i) A rural district (Ardèche,) ii) A district with an industrial economy and low development (Loire) iii) A district with a tertiary economy and high development (Rhône) iv) A district where CRC screening has been implemented for a long time (Côte d’Or,) v) One of the suburban districts of Paris, highly urban (Val-de-Marne).The cluster unit is the “Ilots Regroupés pour l'Information Statistique” (IRIS) zone, or « Clustered Units for Statistical Information» zone. Each district in France is divided into IRIS zones, ie aggregated units for statistical information used as a system for dividing the country into units of equal size (2000 residents per basic unit). IRIS zones eligible for this study were IRIS zones from the 5 districts selected for their low participation rate in CRC screening and with socioeconomic indicators of a deprived population. Deprived IRIS zones inside districts were selected using an ecological deprivation index. The French European Deprivation Index (EDI) was used to determine the socio-economic level of the population living in IRIS zones. French EDI is divided into 5 quintiles; from 1 (least deprived) to 5 (most deprived). For all 5 districts, IRIS zones with an EDI corresponding to a deprived population (score 4 and 5) were all selected for the randomization. The mean number of deprived IRIS zones by district was 384. A total of 1920 deprived IRIS zones were selected.