Design and analysis of studies to reduce the incidence of colon polyps

Decisions regarding the design and analysis of a phase III study to reduce the incidence of colorectal polyps must take into account two complicating factors: the possibility that polyps are missed during screening exams, and variable lengths of follow‐up. In this paper we investigate the effects due to misclassification on the power of statistical tests to detect a change in polyp recurrence rates. We also use Monte Carlo studies to examine the relative efficiency of different methods of adjusting for variable times of follow‐up.