Testing behavioral interventions to optimize participation in a population-based colorectal cancer screening program in Catalonia, Spain.

The aim of the study was to measure the effect of three cost-neutral behavioral interventions on participation compared to the standard invitation letter in a population-based colorectal cancer screening program in 2014. For that purpose, a four-arm randomized field trial was conducted among 5077 individuals aged 50 to 69 years. Over an 8-week period, each week was randomly allocated to the intervention or the control conditions. Individuals assigned to the intervention conditions additionally received a prompt to write down the date to pick up the screening test in a pharmacy. Two of the three intervention groups also included an additional paragraph in the invitation letter on either: 1) the high proportion of individuals participating regularly (social norms condition) or 2) the importance of regular participation (benefit condition).