Individuals who had a positive finding at follow-up sigmoidoscopy, but at the diagnostic endoscopy no adenoma was found (n=3370); individuals who had a positive finding at follow-up sigmoidoscopy, but a diagnostic endoscopy was not performed (n=418); and persons who had a positive finding at follow-up sigmoidoscopy, but the study was unable to obtain any information regarding diagnostic follow-up (n=460) were also excluded.