Reliability block diagrams to model the management of colorectal cancer

The present study aims to show how various medical and nonmedical components contribute to success and failure in the management of colorectal cancer. The first encounter, subsequent diagnosis, and surgical therapy of a patient with Dukes B sigmoid cancer is modeled as a reliability block diagram with a serial and parallel arrangement of various components. The overall probability of a patient with new-onset colorectal cancer to visit a physician, be correctly diagnosed, and undergo successful therapy is 69%. The reduction in the overall success, despite the fact that the majority of components are assumed to function with failure rates of 5% or less, is a reflection of the multitude of serial subsystems involved in the management of the patient. In contrast, the parallel arrangement of subsystems results in a relative insensitivity of the overall system to failure, a greater stability, and an improved performance. Since no medical system functions perfectly, redundancy associated with parallel subsystems assures a better overall outcome. System analysis of health care provides a means to improve its performance.