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The case for case-mix adjustment in practice profiling. When good apples look bad
S Salem-Schatz1, G Moore, M Rucker
1Harvard Community Health Plan, Brookline, MA 02146.
JAMA
|September 21, 1994
Summary
Adjusting for patient characteristics significantly reduces practice variation and identifies fewer outlier physicians. Failing to account for patient case mix can lead to inaccurate assessments of physician performance and misdirected quality improvement efforts.
Area of Science:
- Health Services Research
- Medical Informatics
- Physician Performance Measurement
Background:
- Physician practice profiling is crucial for quality assessment.
- Patient characteristics can influence observed practice patterns.
- Accurate practice profiling requires accounting for patient case mix.
Purpose of the Study:
- To evaluate the impact of patient characteristics on physician practice profiling.
- To assess how adjusting for age/sex versus case mix affects practice variation estimates.
- To determine the influence on identifying outlier physicians and predictors of variation.
Main Methods:
- Retrospective cohort study of 37,830 patients across 52 physician practices.
- Calculation of unadjusted referral rates and adjusted standardized referral ratios.
- Analysis of variation using coefficients of variation and outlier status determination.
Main Results:
- Adjustment for patient characteristics reduced variation by over 50%.
- 75% of age/sex-adjusted outliers were not identified when case mix was considered.
- Predictors of unadjusted referral rates (e.g., physician age, practice tenure) lost significance after adjustment.
Conclusions:
- Failure to adjust for case mix overestimates practice variation and misidentifies outliers.
- Inaccurate profiles can lead to inequitable physician decisions (education, sanctions, employment).
- Misinformation on practice variation can misdirect quality improvement resources.