LAUSR

ABSTRACT In the past decade, risk-adjusted control charts have been widely used to monitor surgical outcomes. However, most existing approaches focus on monitoring shifts in location parameters and may not be able to detect a scale change that is also likely to occur in surgical data. In this article, we derive a weighted score test statistic to construct an exponentially weighted moving average chart and propose a new charting method to simultaneously monitor location and scale parameters. This new chart may be applied to monitoring surgical performance. Simulation results indicate that the proposed method is more efficient than existing methods, such as the risk-adjusted cumulative sum chart, in detecting the heterogeneity of surgical outcomes. A data set from the Surgical Outcome Monitoring and Improvement Program in Hong Kong is used to illustrate the applicability of the proposed chart.