Randomization and blinding procedures
colorectal cancer
COLORECTAL CANCER
Among all IRIS zones from the 5 districts eligible for the study (N = 1920), the participant IRIS were randomly selected with a 2 steps selection process. The centralized randomization was stratified by districts. For the experimental group, one IRIS per district was selected randomly from the eligible IRIS. Then 3 eligible adjacent IRIS were selected accordingly, in order to construct the experimental group. It was mandatory for the experimental group of 4 IRIS to have a continuous geographical setting, since the Navigator was supposed to act in a geographical “puddle-like” unit of action. For the Control group: 4 remote IRIS were randomly selected from the eligible IRIS of the district The randomization was performed at the IRIS level and was performed at once, before the beginning of the study, by an independent statistician. The allocation ratio of experimental and control groups was set at 1:1.The trial was an open trial since no blinding was possible. But individuals not contacted by the navigator and individuals in the control group were blinded to their group, and even blinded to the study. Investigators were blinded to the measurement and collection of the primary outcome.Sample size calculation estimated that the number of IRIS zones needed to meet the objectives of the study was 20 IRIS in the intervention group and 20 in the control group. This estimation relies on the following assumptions: We estimated that the intervention would be relevant if it provided an 8% absolute increase in the colorectal cancer screening participation rate. With a two- sided α risk of 0.05 and a β risk of 0.2, and assuming an intraclass correlation coefficient for clusters of 0.04 and a mean of 500 patients per cluster (assuming an average of 2000 people per IRIS zone and percentage of people between 50 and 75 years equal to 25% of the total population), we needed 20 clusters per arm. This represents: 4 experimental IRIS zones and 4 control IRIS zones per department. For a total of 40*500 = 20 000 patients).