Statistical analysis and sample size calculation
colorectal neoplasia, tumor
REGRESSION, TUMOR, RECRUITMENT
Screening uptake and detection rate of advanced colorectal neoplasia were assessed by intention-to-screen analysis. FDR who did not attend the initial appointment, and thus did not provide information about exclusion criteria, were considered as eligible and were included in the analysis. Individuals who did not comply with the assigned strategy were not allowed to change to the other group.Between-group comparisons of the main outcome were calculated by multivariable logistic regression analysis with adjustment for FDR’s age and sex, allocation of 1 or different screening strategies in the same family, index case tumor location, person (index case or other FDR) who attended the first appointment, and center (categorized as high or low recruiters, if they included more or less than 80 eligible individuals in the study, respectively). Results were reported as odds ratios (OR) with 95% confidence intervals (CI).The detection rate of advanced colorectal neoplasia was the number of subjects with true positive results divided by the number of eligible subjects. The comparison of advanced colorectal neoplasia detection rate between the study groups was calculated by multivariable logistic regression analysis adjusting by the age of the FDR (categorized as having more or less than 54 years of age, according to the median age of participants), sex, and center.Comparisons of continuous variables were performed using the Mann–Whitney U-test. Categorical variables with 2 categories were compared using the χThe study was designed to achieve a 90% power and 95% confidence level for detecting an increase in the proportion of FDR undergoing CRC screening of 10% (from 50% in the colonoscopy group to 60% in the FIT group). According to these assumptions, and considering that up to 5% participants in each group would be lost to follow-up, the estimated sample size was 1,076 individuals (538 per group).When 81% of the estimated sample size was reached, an interim analysis was conducted because recruitment was much lower than expected. Based on the screening uptake of 870 randomized FDR, the futility analysis [