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 Ra = 0.6.) Comment on the performance of the surgical team.