The extended hospital medical staff is essentially a hospital-associated multi-specialty group practice that is empirically defined by physicians' direct or indirect referral patterns to a hospital.9
Here we summarize how we have defined such groups, describe how tightly physicians are affiliated with their hospitals, and show that Medicare beneficiaries' care is highly concentrated within their extended hospital medical staff. We then provide an example of how performance measurement at this level could be carried out.
For this analysis, we assigned physicians and their patients to hospitals using a three-year period of claims (2002–2004) and report utilization measures for calendar year 2003. We assigned physicians to their primary hospital by one of two methods. We assigned the approximately 60 percent of physicians billing Medicare who do inpatient work to the hospital where they provided care to the most inpatients. For physicians who do no inpatient work, we identified all of the Medicare beneficiaries to whom they provided care during the three-year period, and we assigned each physician to the hospital where the plurality of those patients were admitted.
Assignment of patients to hospitals and medical staffs can be carried out using a variety of approaches. Studies of conditions requiring hospitalization (such as myocardial infarction or major surgery) have assigned patients to the hospital where they received their initial inpatient care. Studies of Medicare beneficiaries with severe chronic illnesses have assigned patients based on the plurality of their discharges during a specific period.10
Assessment of primary care performance, however, requires assigning all patients—even those without discharges—to a provider. To define the ambulatory cohorts associated with a group of physicians, we assigned all Medicare beneficiaries to the physician (primary or specialty care) who provided most of their care in the ambulatory setting. Beneficiaries were then assigned to their physicians' primary hospital (and its extended medical staff). Finally, for each hospital, we identified the single other hospital most frequently used by the ambulatory cohort (which we defined as the “secondary” hospital). Consistent with intuition, this is most often a referral hospital.11
Whether it is feasible even to consider the hospital and its extended medical staff as a locus of accountability depends on several empirical questions. (1) Is physicians' work, in fact, largely associated with a single or a predominant hospital? (2) Is Medicare beneficiaries' care sufficiently concentrated within each hospital's extended medical staff that it would be reasonable to consider holding those physicians collectively responsible for their assigned patients' care? (3) Does performance measurement at the medical staff level offer substantial advantages, in terms of either the scope of measures or the sample sizes available?
Is physicians' work concentrated in a single hospital?
summarizes several key aspects of empirically defined hospital medical staffs.
Characteristics Of Extended Hospital Medical Staffs: Size And Distribution Of Extended Hospital Medical Staffs And Their Degree Of Affiliation With Their Primary Hospital, Stratified By Hospital Size And Rural/Nonrural Location
Medical staff size and composition
The medical groups defined by this method appear reasonable in terms of their size and composition. The average U.S. hospital has an extended medical staff of eighty-eight physicians per hundred beds. Larger hospitals and those in nonrural areas have more affiliated physicians. The specialty composition of the affiliated staff is plausibly related to hospital size and location. The average number of primary care physicians per hundred beds is relatively similar across hospitals of differing sizes and in rural and nonrural areas. Nonrural and larger hospitals, however, have more medical specialists, surgeons, and other physicians (such as radiologists and pathologists) per hundred beds.
Degree of physician affiliation
In general, physicians' degree of affiliation with their hospitals is strong. On average, 62 percent of physicians perform inpatient work; the proportion performing inpatient work is slightly greater in smaller and rural hospitals ().12
Of all physicians doing inpatient work, only 60 percent work at a single hospital; however, among those who work at multiple hospitals, three-quarters of their inpatient work is at their primary hospital. Consequently, for physicians who do any inpatient work, 90 percent or more of their inpatient work is at their primary hospital.13
Among the 38 percent of physicians who don't do any inpatient work, more than half of their patients' admissions occur at the hospital to which the physicians were assigned ().
Concentration of patients' care within the extended hospital medical staff
Most importantly, however, Medicare beneficiaries' care is highly concentrated within these empirically defined delivery systems (). On average, 72.7 percent of beneficiaries' physician visits for evaluation and management (E&M) services (inpatient and outpatient) are to physicians within their assigned extended hospital medical staff, and an average of 63.5 percent of all admissions are provided by the primary hospital. Because many services are provided only at larger or more specialized hospitals, we describe the concentration of care not only for their primary hospital (the one to which they are directly assigned) but also for the single other hospital that is most frequently used by a given hospital's Medicare population. Taking the primary and secondary hospitals together, 81.8 percent of E&M services and 76.3 percent of admissions occur within this locally defined delivery system. And although there is some variation in the degree of care concentration, for 90 percent of hospitals (which account for 98 percent of assigned beneficiaries), the proportion of physician services provided by the primary hospital medical staff is greater than 44 percent, and the proportion provided by the primary and secondary hospital medical staffs is greater than 65 percent (data not shown).
EXHIBIT 2 Medicare Beneficiaries' Reliance On Their Hospital And Its Extended Medical Staff: Degree To Which Beneficiaries' Care Is Provided By The Extended Hospital Medical Staff And The Hospital To Which They Were Empirically Assigned During 2003, Stratified (more ...)
The rationale for considering concentration of care within both primary and secondary hospitals is most apparent when one focuses on small hospitals (both rural and nonrural) and their surgical admissions. In small rural hospitals, for example, only 15.7 percent of surgical admissions for assigned patients occur at the rural hospital, but 39 percent occur at the identified referral hospital (for a total of 54.7 percent of surgical admissions at either one). Also, 82.1 percent of medical admissions occur at either the primary or secondary hospital. The overall patterns thus reveal a high degree of care concentration, even in rural areas.
Measuring performance at the hospital medical staff level
To further explore the technical feasibility and potential advantages of using the hospital and its extended medical staff as a locus of accountability, presents data on several dimensions of performance that are made possible (or more tractable) when the level of analysis is the extended hospital medical staff. For this example, hospitals and their extended medical staffs have been aggregated into five groups based upon their 2000–02 experience treating patients with heart attacks, colon cancer, and hip fracture. (These are the same study populations used in our earlier work in which we compared longitudinal costs and outcomes across regions.)14 High-performing hospitals
were defined as those in the lowest quartile on both risk-adjusted one-year mortality and risk-adjusted one-year costs (using standardized prices); low-performing hospitals were those in the bottom quartile on both measures, while the other three groups had intermediate levels of performance.15
Longitudinal Experience Of Ambulatory Medicare Beneficiaries Assigned To Extended Hospital Medical Staffs (EHMSs) In 2003, Stratified By Performance On Adjusted Mortality And Price-Standardized Costs For Their Hospitalized Cohorts In 2000–02
focuses on the performance of the extended hospital medical staff in treating their entire assigned ambulatory population during the year after the assignment to performance levels. Quality of ambulatory care is generally higher in the hospitals that had demonstrated lower risk-adjusted mortality: Women are more likely to have undergone mammography (52.8 percent in the highest-performing groups versus 42.6 percent in the lowest), and diabetic testing (for blood sugar or retinopathy) is somewhat better in higher-performing groups.
Higher-performing medical staffs also have much lower use of institutional settings, with fewer hospital discharges, fewer skilled nursing facility (SNF) discharges, and fewer total Medicare-reimbursed institutional days. They also experience fewer care transitions.
Finally, higher-performing hospitals also have lower risk-adjusted longitudinal costs for their ambulatory Medicare patients: Longitudinal costs in the lowest-performing hospital group were 26 percent higher than in the highest-performing hospital group ($5,625 versus $4,467).
The bottom half of presents data on the relative coherence of the extended hospital medical staffs in different performance groups: Higher-performing extended medical staffs appear to be somewhat more tightly affiliated with their hospital (that is, they do more of their work within their primary hospital); their patients receive more of their care from the extended medical staff itself; and the patients treated by the lower-performing extended hospital medical staffs see, on average, more different physicians.
These comparisons of performance are presented primarily as a test of concept (do potentially important differences emerge?) and must be interpreted cautiously. Our claims-based risk-adjustment methods might not have adequately accounted for differences in health status across systems. We used a limited set of quality measures to identify high-performing systems. Prior research indicates that many quality indicators are poorly correlated at the provider level, and efforts to define truly high-performing systems will require comprehensive performance measurement along multiple dimensions, to ensure that providers who appear to be high-performing on one dimension are not poor performers on other important dimensions that might be harder to measure.16
As we discuss below, these technical issues could be overcome with more-comprehensive measures of both underlying risk and system performance.
highlights another major technical advantage of focusing on the extended hospital medical staff for performance measurement. As mentioned above, prior studies have raised questions about the feasibility of assessing performance at the individual physician level. presents the numbers of physicians caring for patient panels of various sizes, either as individuals or as members of an extended hospital medical staff. Half of the physicians who are the predominant providers for Medicare beneficiaries have fewer than fifty beneficiaries in their empirically defined panels. The middle columns make the obvious point that the proportion of all physicians who can thus be assessed for their contribution to the care of chronically ill patients (in the sense of being the responsible physician) is even smaller (largely for the obvious reason that they are in specialties that do not provide primary care, such as radiology or pathology). In contrast, when the focus of assessment is expanded to the extended hospital medical staff, 98 percent of physicians are affiliated with physician groups that serve Medicare populations of more than 500 beneficiaries. Even if the analysis is restricted to patients with heart failure, diabetes, or coronary artery disease, 95 percent of physicians are caring for populations of more than 500 Medicare beneficiaries—more than enough for reliable performance assessment.17
Percentage Of Physicians With Assigned Ambulatory Patients, According To The Size Of The Medicare Patient Panels They Served During 2003, When Analyzed At The Individual Physician Level And At The Extended Hospital Medical Staff (EHMS) Level