The predicted mortality of cardiac surgery patients in an intensive care unit, based on their APACHE score, is found based on a logistic regression model applied to patients over a four-year period. Table 7-32 shows the predictive pre-operative mortality for 25 recent patients, along with the observed outcome after surgery, where a value of 0 indicates that the patient survived while a value of 1 indicates that the patient died. Construct a risk-adjusted cumulative sum chart for patient mortality to determine if there has been an improvement. (Use the odds ratio under the alternative hypothesis to be R_a = 0.6.) Comment on the performance of the surgical team.

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TABLE 7-32 Predicted and Observed Mortality of Patients Observed Mortality Patient Predicted Patient Predicted Observed Number Mortality Number Mortality Mortality 1 0.28 14 0.44 2 0.62 15 0.58 3 0.45 1 16 0.32 4 0.36 17 0.75 5 0.72 18 0.84 6 0.84 1 19 0.69 7 0.26 20 0.82 1 8 0.54 21 0.72 9 0.40 22 0.64 10 0.74 1 23 0.62 11 0.49 24 0.73 12 0.55 25 0.82 13 0.37