Modeling in rare diseases is often challenging; however, a number of approaches are available to support the development of model structures and the collation of input parameters and to manage uncertainty.

Colorectal cancer remains the second leading cause of cancer death in the United States. To fully realize the benefits of early detection of colorectal cancer, screening rates must improve. This study assessed differences in beliefs (from the Health Belief Model) by stage of screening behavior adoption (based on the Transtheoretical Model of Change) as a foundation for intervention development. More people were in the precontemplation stage (not thinking about having the screening test) for fecal occult blood test and sigmoidoscopy versus contemplation (thinking about having the test) or action (adherent with screening). Those in precontemplation stage for fecal occult blood test had lower perceived risk than those in contemplation, lower perceived benefits than those in action, and higher barriers than both those in contemplation and those in action. For sigmoidoscopy stage of readiness, again, precontemplators had lower perceived risk and self-efficacy than contemplators and higher barriers than both contemplators and actors. Given the popularity of the transtheoretical model and the success of stage-based interventions to increase other cancer screening, especially mammography, we should begin to translate such effective interventions to colorectal cancer screening. As such, this study is one of very few to quantify beliefs across stages of colorectal cancer and identify significant differences across stages, laying the foundation for the development and testing of stage-based interventions. KeywordsColorectal cancer screening; Early detection; Health belief model; Stages of change Colorectal cancer (CRC) is the third most common cancer in men and women in the United States. About 145,290 new cases are expected this year, with an estimated 56,290 deaths. 1 Survival from CRC is inversely related to stage at diagnosis; late-stage diagnosis is related to lower survival. Regular screening could offset this by facilitating early detection, leading to early-stage diagnosis. However, current screening rates remain suboptimal. Recent data indicate that fecal occult blood test (FOBT) screening rates were 17% for men and women and 5-year screening rates for sigmoidoscopy/colonoscopy were less than 33.5% for men and 27% for women.2 , 3 To realize fully the benefits of early detection, screening rates must increase considerably. Clearly, there is a need for interventions to facilitate participation in screening. Indeed, early-stage diagnosis is associated with a 90% 5-year survival rate, but 3. Identify specific beliefs significant to stage of behavior adoption for FOBT and sigmoidoscopy.The TTM, which states that behavior change occurs in a series of incremental stages, has been used extensively to study health promotion behaviors such as exercise, smoking cessation, and mammography use 5-8 but is less used in CRC screening research. The HBM, which posits that behavior change is influenced by a certain combination of beliefs, has been used extensively in cancer screening research, including CRC screening. Combin...