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Article Excerpt
Racial disparities in outcomes and processes of health care have been documented for a wide spectrum of illnesses (Institute of Medicine 2002). Recent studies demonstrate that disparities may be attributed, in part, to differences in clinical practice across regions (Skinner et al. 2003; Baicker et al. 2004; Haas et al. 2004; Groeneveld, Heidenreich, and Garber 2005) or differences in the use of high-quality providers within regions (Gregory et al. 1999; Bradley et al. 2004; Schelbert et al. 2005). Such disparities may, in turn, be a symptom of racial segregation that occurs in the health care delivery system or by residence.
Previously, residential segregation has been linked to higher mortality for black populations (Hart et al. 1998; Collins and Williams 1999), and, to specific health conditions, including cardiovascular disease (Cooper 2001). Residential segregation is believed to affect health indirectly through environmental and individual factors such as poor housing conditions, lack of information, health behaviors, and stress (Schulz et al. 2005; Payne-Sturges et al. 2006). Utilization and outcomes of specific health services may also be impaired if racially concentrated neighborhoods face limited access to high-quality providers, or if social pressures within such neighborhoods deter the use of services deemed unacceptable by neighborhood norms.
While residential segregation likely plays a key role in segregating the health delivery system, other factors contribute to segregation of hospital services independent of residence. Historically, hospitals were racially segregated in the South and most northern cities before the 1960s (Halperin 1988; Smith 1998, 2004). While sanctioned forms of hospital segregation were essentially eliminated during the 1960s, de facto segregation remains, partly due to social and economic pressures that are unique to health care. First, hospitals are predominantly voluntary in ownership and thus insulated from public scrutiny and political control. Until recently, external monitoring efforts, such as those by JCAHO, focused almost exclusively on structure (e.g., staff credentials). Second, medical staffs within hospitals have wide latitude in assigning clinical privileges. If such latitude results in fewer admitting privileges for physicians who treat blacks, access to hospitals for patients of black physicians may be compromised. Hospitals and individual physicians may also limit the patients they treat through managed care contracting, payment criteria, or physical location. Such activities may make sense from a "business" perspective, but they can have divisive effects on patient populations. Other factors that may divide hospitals racially include racial differences in physician referrals, transportation systems, hospital emergency department capacity, institutional discrimination, and patient preferences. Hospital segregation may, in turn, impact health outcomes and service utilization differently than residential segregation through racial differences in access to high-quality providers, specialized services, and medical practice patterns.
Sociological literature defines multiple dimensions of segregation (Massey and Denton 1988). The most popular dimension reflects the evenness of the population distribution across units. Using this dimension, hospital segregation exists if patients are distributed unevenly by race across hospitals. A second dimension of segregation reflects the isolation of a minority group to the majority. Markets in which black patients are unlikely to be exposed to white patients within hospitals are segregated on this dimension. A geographic market can be segregated on multiple dimensions, or it may be segregated on one dimension but not another. For example, black patients may be evenly distributed across hospitals in a market but experience little exposure to white patients if a large proportion of the market is black.
Isolation and uneven distribution may impact disparities uniquely, although there is likely significant overlap. Isolation may impact disparities if hospitals in which blacks have little exposure to whites are under-funded, limiting the availability of specialized services. Isolated black patients may also have lower levels of trust for white providers or feel unwelcome by white providers, making them disinclined to use the services of majority white hospitals, even if such hospitals are available to them (Marschall and Stolle 2004). Physicians treating those patients may be equally isolated, and therefore unlikely to refer patients to majority white hospitals with more services. Finally, an isolated black medical community may develop medical practice patterns that reflect the norms of the populations they serve--such practices may differ from those of less isolated communities. Dissimilar distribution of blacks across hospitals may impact disparities similarly, if the uneven distribution results in racial isolation. In contrast, uneven distribution may actually facilitate utilization if minority populations perceive a cultural affinity with a particular hospital.
Figure 1 provides a framework for investigating the relationship between segregation and disparities in the utilization and outcomes of health services. Residential unevenness and isolation impact racial differences in environmental and individual factors such as poverty, proximity to services, housing conditions, individual stress, and social norms. These residential factors also impact hospital unevenness and isolation, which may be magnified further by other delivery system factors, including physician referral patterns, third-party payer contracts, and patient preferences. Ultimately, disparities in health care utilization and outcomes result.
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This study investigates segregation, defined as racial unevenness and racial isolation, and disparities in treatment of acute myocardial infarction (AMI). Hospital discharge data for black and white patients admitted for AMI during 2004-2005 were used to calculate two measures of hospital segregation. Analyses investigated the relationship of hospital segregation measures to each other, as well as to residential segregation, and the relationship to disparities in the use of revascularization after AMI. AMI was chosen as the disease paradigm because of the extensive evidence documenting disparities in treatment of AMI (Barnato et al. 2005; Cromwell et al. 2005; Vaccarino et al. 2005; Popescu, Vaughan-Sarrazin, and Rosenthal 2007).
METHODS
Patient Population
Patients were identified using Medicare Provider Analysis and Review (MedPAR) data files. MedPAR files contain all Medicare fee-for-service hospitalizations and include patient demographics and zip code, ICD-9-CM diagnoses and procedure codes, admission source (e.g., transfer from another hospital), admission and discharge dates, hospital discharge disposition, date of death, and hospital identifier. Records for black and white patients with primary ICD-9-CM diagnosis codes 410.xx admitted during 2004-2005 were identified in the MedPAR files (N = 607,664). Patients were excluded if they were transferred from another acute care facility (n = 89,243) or resided outside the market of the admitting hospital (n = 60,051), leaving 458,370 patients.
Health Care Markets
Regional markets for hospital care were defined using hospital referral regions (HRR's), which represent 306 geographic markets for tertiary health care and were defined using zip codes to reflect patient flows for major surgery (http://www.dartmouthatlas.org). HRR characteristics were obtained from the American Hospital Association 2005 Survey...
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