The c statistic for the model was 0.74, which indicates a relatively high level of accuracy.57 Several risk-assessment schemes have been developed to assist in identifying patients with severe CAD, including left main disease, although several of these studies are up to 2 decades old. One study70 identified 8 clinical characteristics that are important in estimating the likelihood of severe IHD: typical angina, previous MI, age, sex, duration of chest pain symptoms, risk factors (hypertension, diabetes mellitus, hy- perlipidemia, and smoking), carotid bruit, and chest pain frequency. A subsequent study71 provided detailed equations to predict both severe IHD and survival on the basis of clinical parameters. One study249 developed a simple risk score for predicting severe (left main or 3-vessel) CAD that was based on 5 clinical variables: age, sex, history of MI, presence of typical angina, and diabetes mellitus with or without insulin use. This same score was validated subse- quently for prognostic purposes.250,251 This score can be easily memorized and calculated (Figure 11) and yields an integer ranging from 0 to 10.57 The score can be applied to determine if a patient is more suitable for stress testing or possibly (in appropriate patients who are at highest risk) for proceeding directly to coronary angiography. Each curve shows the probability of severe IHD as a function of age for a given cardiac risk score. As shown on the Figure 11 graph, some patients have a high likelihood (.50%) of having severe disease for which revascularization might improve survival on the basis of clinical parameters alone. 