Any measurement in which the number of individuals in a study population that display colorectal tumors at a point in time or develop colorectal tumors within a determined period of time are compared to the total number of individuals in the study population. Often expressed as a percentage but could be expressed as a ratio. Colorectal tumors are abnormal growths of tissue resulting from uncontrolled, progressive multiplication of cells and serving no physiological function, which occur in the large intestine, the distal portion of the alimentary canal, especially in the colon and/or rectum, the segment of the large intestine between the cecum and the anal canal.