Perception of Colorectal Cancer Risk does not Enhance Participation in Screening.

High participation is a key requirement for effective cancer screening. Many strategies to improve participation hold that a person's knowledge and beliefs dictate screening behavior. We compared perception of colon cancer risk in participants and nonparticipants in a population-based study of screening colonoscopy, and also assessed past screening behavior. Surprisingly, while past screening behavior was a predictor of participation, we found that participants perceived their risk of colorectal cancer to be significantly and substantially lower than the real figure and that of nonparticipants. Our data suggest that health promotion strategies aimed at improving health knowledge may not be effective in improving population screening rates.