Original Research A modified method for estimating volume–outcome relationships: application to percutaneous coronary intervention

OBJECTIVE: The objective of the current study was to propose an alternative method for measuring individual operator and peer volumes to use as predictors for adverse outcomes. STUDY DESIGN: A retrospective analysis was performed to assess the volume-outcome relationship for percutaneous coronary intervention (PCI) performed in New York State between 1996 and 1999. This relationship was calculated using a modified method whereby physician volume was calculated using the previous year's volume, and hospital volume was calculated after subtracting the operator of interest's annual volume from the total. The primary outcome of interest was in-hospital mortality. RESULTS: Using the modified method, the odds ratio (OR) of in-hospital mortality was 0.74 (95% confidence interval (CI) 0.55-0.99; p=0.04) for cardiologists who performed 75-174 procedures annually and 0.80 (95% CI 0.61-1.04; p=0.1) for cardiologists who performed > or =175 procedures annually compared with the lowest-volume operators. With the conventional approach to volume measurement, no relationship between cardiologist volume and mortality was found. Patients who underwent PCI in hospitals where their physician's peers had an annual volume of 600-999 or > or =1,000 cases had a significantly reduced odds of mortality (OR = 0.73; 95% CI 0.57-0.92; p=0.01; and OR = 0.77; 95% CI 0.62-0.95; p=0.01) compared with patients treated by physicians with an annual peer volume of <600 cases. The conventional method did not detect any significant correlation between hospital volume and in-hospital mortality. CONCLUSION: The alternative approach to measuring cardiologist and peer volumes proposed in this study leads to more precise estimates of volume-outcome relationships than the conventional approach.