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How Many Doctors Does It Take to Treat a Medicare Patient?

NEJM Study: Fragmented Care Poses Serious Hurdle to Medicare Pay-for-Performance (P4P) Initiatives

News Release
March 14, 2007

Alwyn Cassil (202) 264-3484 or

WASHINGTON, DC—Medicare beneficiaries’ care is spread over so many physicians that determining which physician should qualify for additional payment is a moving target under current pay-for-performance (P4P) designs, according to a study by researchers at the Center for Studying Health System Change (HSC) and Memorial Sloan-Kettering Cancer Center (MSKCC) in the March 15 New England Journal of Medicine.

As Medicare moves to develop a national physician P4P program, two assumptions underpin successful implementation: that claims data can be used to retrospectively assign patients to physicians or practices with primary responsibility for their care, and that physicians can be held responsible for a meaningful percentage of the patients they treat and the visits they bill for.

The reality, however, is that many different physicians and practices provide care to each elderly Medicare patient, so identifying which provider is responsible for which patient is difficult. Because of this, physicians
also are unlikely to have a critical mass of patients who are their primary responsibility, and about a third of the patients they would be held responsible for will switch to a different provider the next year anyway, the study found.

A Medicare patient seen by the typical physician in the nationally representative study was treated by seven different doctors in four different medical practices in a given year, the study found. And only about 35 percent of beneficiaries’ visits were with the doctor held responsible for their care under the most common P4P methodology used to assign patients to physicians. Moreover, for 33 percent of beneficiaries, the assigned physician and practice changed from year to year.

"The study raises serious questions about how meaningful a Medicare pay-for-performance program would be for patients in the current fee-for-service system where care is so widely dispersed," said Hoangmai H. Pham, M.D., M.P.H., the study’s lead author and senior health researcher at HSC, a nonpartisan policy research organization funded principally by The Robert Wood Johnson Foundation.

"If physicians don’t know which patients they have primary responsibility for ahead of time, and Medicare only figures this out after the fact, then it is hard to envision how P4P incentives will motivate physicians to improve the quality of care they deliver," Pham said. "Physicians would not know which patients to target with particular services or whether making large investments, such as in health information technology, will really pay off if most of the patients they are responsible for don’t stay assigned to them over time."

The study, "Care Patterns in Medicare and Their Implications for Pay for Performance" is based on HSC’s 2000-01 nationally representative Community Tracking Study Physician Survey, which collected information from 12,000 practicing physicians, and Medicare claims information on beneficiaries these physicians treated in 2000-02. Data on physicians and patients were linked with the use of the physicians’ unique provider identification number, and a total of 8,604 physicians and 1,787,454 elderly Medicare patients were included in the study.

The study also found that patients with chronic conditions, such as heart disease or diabetes, saw more physicians than the typical Medicare beneficiary-those with heart disease saw a median of 10 physicians in six different practices, while those with diabetes saw eight physicians in five different practices. Moreover, care was more dispersed as a patient’s number of chronic conditions increased. Patients with seven or more conditions saw 11 physicians in seven practices, while those with fewer than three conditions saw three physicians in two practices.

"Improving the care of patients with multiple chronic illnesses is where P4P has its greatest potential-but ironically, implementation will be more challenging, because these patients see even more doctors," said Peter B. Bach, M.D., M.A.P.P., coauthor of the study and a researcher in the Department of Epidemiology and Biostatistics at MSKCC in New York City. "We suspect that in some of these cases, no one doctor is able to take central responsibility for coordinating care, but that is what will be needed for P4P to work."

Using a variety of different methods to assign patients to physicians or practices, the study concluded that typically primary care physicians would be held accountable for 39 percent of the Medicare patients they treat and 62 percent of Medicare visits they bill, while medical specialists, who often provide more costly care, would be held accountable for 12 percent of the Medicare patients they treat and 20 percent of the total Medicare visits they bill.

Instead of using claims data to retrospectively assign patients to physicians, the authors suggest that Medicare consider prospectively assigning patients to physicians and practices to establish clearly which providers will be held accountable for coordinating patients’ care. "Prospective designation of the responsible providers, even if voluntary, implies some limitation of the freedom of both patients and physicians to choose the physicians with whom they work, but it would have the benefit of aligning physician, patient and payer expectations of care relationships," the article concludes.

The study was coauthored by Deborah Schrag, M.D., M.P.H., of MSKCC; Ann O’Malley, M.D., M.P.H., of HSC; and Beny Wu, M.S., of Social Scientific Systems; and was supported by grants from the National Institute on Aging and the Robert Wood Johnson Foundation.

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The Center for Studying Health System Change is a nonpartisan policy research organization committed to providing objective and timely research on the nation’s changing health system to help inform policy makers and contribute to better health care policy. HSC, based in Washington, D.C., is funded principally by the Robert Wood Johnson Foundation and is affiliated with Mathematica Policy Research, Inc.

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Memorial Sloan-Kettering Cancer Center is the world’s oldest and largest private institution devoted to prevention, patient care, research and education in cancer. MSKCC scientists and clinicians generate innovative approaches to better understand, diagnose and treat cancer. MSKCC specialists are leaders in biomedical research and in translating the latest research to advance the standard of cancer care worldwide. For more information, go to



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