CLINICAL STUDY: BYPASS SURGERY
Challenges in comparing risk-adjusted bypass surgery mortality results
Results from the Cooperative Cardiovascular Project
Eric D. Peterson, MD, MPH, FACC*,
Elizabeth R. DeLong, PhD*,
Lawrence H. Muhlbaier, PhD*,
Allison B. Rosen, MD, MPH*,
Hope E. Buell, MS*,
Catarina I. Kiefe, MD, PhD and
Timothy F. Kresowik, MD, MPH
* The Duke Outcomes Research and Assessment Group, Duke University Medical Center, Durham, North Carolina, USA
The Alabama Quality Assurance Foundation, and the University of Alabama at Birmingham Center for Outcomes and Effectiveness Research and Education, Birmingham, Alabama, USA
The Iowa Foundation for Medical Care, West Des Moines, Iowa, USA
Manuscript received July 26, 1999;
revised manuscript received June 1, 2000,
accepted July 14, 2000.
Reprint requests and correspondence: Dr. Eric D. Peterson, Box 3236, Duke University Medical Center, Durham, North Carolina 27710
OBJECTIVES
We sought to evaluate the predictive accuracy of four bypass surgery mortality clinical risk models and to examine the extent to which hospitals risk-adjusted surgical outcomes vary depending on which risk-adjustment method is applied.
BACKGROUND
Cardiovascular "report cards" often compare risk-adjusted surgical outcomes; however, it is unclear to what extent the risk-adjustment process itself may affect these metrics.
METHODS
As part of the Cooperative Cardiovascular Projects Pilot Revascularization Study, we compared the predictive accuracy of four bypass clinical risk models among 3,654 Medicare patients undergoing surgery at 28 hospitals in Alabama and Iowa. We also compared the agreement in hospital-level risk-adjusted bypass outcome performance ratings depending on which of the four risk models was applied.
RESULTS
Although the four risk models had similar discriminatory abilities (C-index, 0.71 to 0.74), certain models tended to overpredict mortality in higher-risk patients. There was high correlation between a hospitals risk-adjusted mortality rates regardless of which of the four models was used (correlation between risk-adjusted rating, 0.93 to 0.97). In contrast, there was limited agreement in which hospitals were identified as "performance outliers" depending on which risk-adjustment model was used and how outlier status was defined.
CONCLUSIONS
A hospitals risk-adjusted bypass surgery mortality rating, relative to its peers, was consistent regardless of the risk-adjustment model applied, supporting their use as a means of provider performance feedback. Designation of performance outliers, however, can vary significantly depending on the benchmark and methods used for this determination.
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Abbreviations and Acronyms
| | CABG | = coronary artery bypass surgery | | CCP | = Cooperative Cardiovascular Project | | O/E | = ratio of observed mortality to expected mortality | | RS | = risk score |
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