A Control Chart Method for Simultaneously Monitoring the Average Level and Stability of Surgical Quality

Good and stable surgical quality is of great significance to ensure the life safety of patients and spare patients unnecessary health burdens. The variable life-adjusted display (VLAD) is a popular assessment method for surgical quality and some VLAD-based control charts have been proposed to motivate the quality improvement. However, existing charts can only monitor the average level of surgical quality by detecting the changes of VLAD’s mean, but lack a mechanism to monitor the stability based on VLAD’s variance. The volatile surgical quality which can hardly be considered good will make existing charts provide delay alarms. Therefore, in this paper, we propose a risk-adjusted exponential weighted moving average (EWMA) control chart to monitor the mean and variance of VLAD simultaneously, named MVV-EWMA. Firstly, we give the explicit form of VLAD’s variance. Then, the EWMA statistics for the mean and variance are respectively constructed and integrated by the generalized likelihood ratio test. Moreover, two auxiliary mechanisms are adopted to enhance MVV-EWMA’s monitoring ability. Both the results of simulation and case study show that MVV-EWMA is not only able to effectively monitor the stability of surgical quality, but also has the best performance compared to existing chart.