We introduce a technique for patient mix-adjusting &xmacr; charts and compared differences between unadjusted and patient mix-adjusted results. Our data came from coronary artery bypass graft (CABG) surgery patients at Baptist Medical Center, Oklahoma City, Oklahoma. We first developed an &xmacr; control chart to compare monthly changes in CABG surgery costs and then used a published model to patient mix-adjust our &xmacr; control chart information. Before adjustment, the average log costs for three of ten months were outside the 90% control limit lines, and there was a trend toward increasing costs. After adjustment, two months had average costs outside the 90% lower control limit lines, and the trend toward increasing costs had been explained by differences in patient acuity.
