Any measurement in which the number of individuals in a study population that display colonic aganglionosis at a point in time or develop colonic aganglionosis 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. Colonic aganglionosis is the absence of parasympathetic ganglion cells in any or all of the myenteric plexus, a network of autonomic nerve fibers within the tunica muscularis of the wall of the alimentary canal in general and of the colon in particular. The colon is the segment of the large intestine between the cecum and the rectum.