Profiling Care Provided by Different Groups of Physicians: Effects of Patient Case-Mix (Bias) and Physician-Level Clustering on Quality Assessment Results

  1. Sheldon Greenfield, MD;
  2. Sherrie H. Kaplan, PhD, MPH;
  3. Richard Kahn, PhD;
  4. John Ninomiya, MS; and
  5. John L. Griffith, PhD
  1. From New England Medical Center and Tufts University School of Medicine, Boston, Massachusetts; American Diabetes Association National Office, Alexandria, Virginia; and University of California, San Diego, California.

    Abstract

    Background: Patient characteristics (case-mix bias) and physician-level variation (clustering) are often overlooked in profiling the quality of care provided by different groups of physicians, such as specialties.

    Objective: To examine the effect of case-mix bias and physician-level clustering on differences in quality of diabetes care between specialty groups participating in the American Diabetes Association's Provider Recognition Program.

    Design: Retrospective record review of both process and outcome measures over 1 year and a cross-sectional patient survey. The sample included 29 solo and group practice sites in diverse regions of the United States. Of the 29 sites, 15 were endocrinology sites and 14 were primary care sites.

    Patients: 1750 adults with diabetes.

    Measurements: Process measures included frequency of hemoglobin A1c, lipid, and urine protein testing; blood pressure measurement; and foot and eye examinations. Outcome measures included A1clevel, blood pressure, lipid levels, and patient satisfaction. Patient case-mix variables included age, sex, health status, level of education, ethnic minority status, and duration of diabetes.

    Results: Unadjusted differences between endocrinologists and generalists were statistically significant for most process and outcome measures. Inclusion of patient case-mix variables reduced the statistical significance of specialty differences for some quality measures. After accounting for the substantial physician-level clustering, observed differences between specialties were no longer statistically significant for any of the quality measures except patient satisfaction.

    Conclusions: The findings underscore the importance of designing physician profiling studies with sufficient power to account for physician-level variation (clustering) as well as patient case-mix. Studies that are not designed with both sufficient numbers of physicians and patients per physician may distort differences in quality of care between physician groups.

    Article and Author Information

    • Disclaimer: The views expressed in this manuscript are those of the authors and do not necessarily reflect those of the American Diabetes Association.

    • Grant Support: By the American Diabetes Association, Alexandria, Virginia.

    • Acknowledgments: The authors thank the American Diabetes Association Provider Recognition Steering Committee for guidance and leadership in facilitating this study; the Health Outcomes Institute, particularly David Radosevich, PhD, and Michael Huber, for invaluable assistance and support; Grace A. Connolly, JD, for editorial input; and Elaine Ackerson for help with preparation of the manuscript.

    • Requests for Single Reprints: Sheldon Greenfield, MD, Primary Care Outcomes Research Institute, Tufts University School of Medicine, M&V 1, 136 Harrison Avenue, Boston, MA 02111; e-mail, sheldon.greenfield{at}tufts.edu.

    • Current Author Addresses: Drs. Greenfield and Kaplan: Primary Care Outcomes Research Institute, Tufts University School of Medicine, M&V 1, 136 Harrison Avenue, Boston, MA 02111.

    • Dr. Kahn: American Diabetes Association, 1701 North Beauregard Street, Alexandria, VA 22311.

    • Mr. Ninomiya: 351 Longden Lane, Solana Beach, CA 92075.

    • Dr. Griffith: Biostatistics Research Center, New England Medical Center, 750 Washington Street, NEMC 063, Boston, MA 02111.

    • Author Contributions: Conception and design: S. Greenfield, S.H. Kaplan, R. Kahn, J.L. Griffith.

    • Analysis and interpretation of the data: S. Greenfield, S.H. Kaplan, R. Kahn, J. Ninomiya, J.L. Griffith.

    • Drafting of the article: S. Greenfield, S.H. Kaplan, R. Kahn.

    • Critical revision of the article for important intellectual content: S. Greenfield, S.H. Kaplan, R. Kahn, J.L. Griffith.

    • Final approval of the article: S. Greenfield, S.H. Kaplan, R. Kahn.

    • Provision of study materials or patients: R. Kahn.

    • Statistical expertise: S.H. Kaplan, J. Ninomiya, J.L. Griffith.

    • Obtaining of funding: S. Greenfield, R. Kahn.

    • Administrative, technical, or logistic support: R. Kahn, J. Ninomiya.

    • Collection and assembly of data: R. Kahn, J. Ninomiya.

    Summary for Patients

    • Summaries for Patients:Comparing the Quality of Diabetes Care by Generalists and Specialists Ann Intern Med January 15, 2002 136:I42
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    1. Ann Intern Med January 15, 2002 vol. 136 no. 2 111-121
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