Colorectal cancer (CRC) is the second leading cause of cancer death in the US. Screening is effective in reducing CRC mortality through the early detection of cancers as well as CRC incidence through the detection and removal of precancerous adenomatous polyps (adenomas). Colonoscopy is the most utilized CRC screening test in the US with an estimated 10 million performed annually. Unfortunately, up to 20% of procedures are incomplete due to inadequate bowel cleanliness, which is associated with missed neoplastic lesions, prolonged procedure duration, and higher complication rates. Despite the high incidence of incomplete colonoscopies due to inadequate bowel cleanliness (~2 million per year) and the potential down-stream consequences, there are limited data on the management of these patients and a paucity of guidelines to help clinicians. The optimal timing of rescreening following an incomplete colonoscopy is unknown, and it is unclear if patients should repeat screening colonoscopy or whether screening with a stool-based test would yield similar outcomes. The goal of the proposed research is to reduce unnecessary testing related to screening colonoscopy by identifying the optimal management strategy for patients who undergo a screening colonoscopy that is limited by inadequate bowel preparation cleanliness. Specifically, we will incorporate bowel preparation quality into an existing microsimulation model - the Simulation Model of CRC (SimCRC) -- and then evaluate the comparative effectiveness of alternative management strategies for patients who undergo a screening colonoscopy that is limited by inadequate bowel preparation. The management strategies will include repeating colonoscopy at varying intervals (e.g. 1, 3, 5, or 10 years) and switching to fecal immunochemical testing (FIT), a stool-based test which does not require any bowel preparation and may have better adherence rates. We will evaluate health outcomes over a 10-year and lifetime horizon. The findings from the proposed research will inform future management recommendations for the large number of patients who undergo a screening colonoscopy limited by a less than optimal bowel preparation and serve as a basis for a future R01 application that tests the dominant strategies in clinical trials. Furthermore, the modified model will have applications beyond the current project including the ability to more accurately simulatecosts and utilization of colorectal cancer screening.