The Relationship between Hospital Case Volume and Outcome from Carotid Endartectomy in England from 2000 to 2005

Mortality-Control Chart – Elective CEA. In-patient death rate (drate) against hospital case volume in five years. The horizontal line represents the national mean mortality rate over five years. Upper and lower 95% confidence intervals from the mean are shown. Each point represents the mortality rate over five-years at an individual hospital. There were several low volume hospitals with mortality rates above the 95% confidence interval and the national mean mortality rate.

Safety Chart for Elective CEA comparing the mortality rate at a hospital to twice that elsewhere. Relative risk of mortality less than elsewhere are green, RR mortality 1-2 times greater than elsewhere (blue) and more than twice elsewhere (red). Control bands represent p-values of 0.05. Each point represents the log₁₀odds of the p-value for the relative risk of mortality compared to twice that elsewhere. When a point lies above the upper control band this represents evidence of danger. When a point lies below the lower control band this represents evidence of safety. Points between the control bands provide insufficient evidence of safety or danger. Six hospitals had evidence that their mortality rate was more than twice that elsewhere, and therefore demonstrated ‘danger.’ Some hospitals provided evidence of safety based on the number of cases and number of deaths. These hospitals are shown in green and lie below the lower control limit. A minimum of 150 cases in five years (30 per annum) were required in order to demonstrate safety.