This study represents the first comprehensive analysis of hospital segregation. Using AMI as the disease paradigm, we find significant variation in segregation levels in 105 markets, with substantial disagreement using the Dissimilarity and Isolation Index. For example, seven markets with high hospital Dissimilarity had low Isolation. These markets tended to have one or two large hospitals serving the majority of black persons in the market (accounting for the high Dissimilarity), but a low overall proportion of black patients, suggesting that blacks are not isolated from the white majority. There were also 10 markets with low Dissimilarity but high Isolation for AMI—all but one of these markets was located in the South. In these markets, black patients may be spread approximately evenly across hospitals (i.e., low Dissimilarity), but the overall proportion of blacks patients is high.
Not surprisingly, hospital segregation was correlated with residential segregation, using either measure. Nevertheless, only slightly more than 50 percent of either hospital segregation measure was explained by residential segregation, suggesting the importance of factors other than geographic proximity in hospital selection. Notably, only 57 percent of white and 52 percent of black patients in our study were admitted to the hospital closest to their residence zip code—a surprising finding given the expectation that patients experiencing AMI be admitted to the closest hospital. The frequent use of diversion status by inner-city hospitals may play a role in the use of distant hospitals (Hoot and Aronsky 2008
), but this does not explain the uneven distribution by race. Hospital Dissimilarity also increased with higher managed care penetration and income, suggesting that the racial distribution across hospitals is explained in part by payer status. Finally, hospital Dissimilarity increases significantly as the number of hospitals and population increase—an expected finding given that the potential for segregation increases in larger markets. The strongest correlate to hospital Isolation was the percent of the population black—so strong, in fact, that the Isolation Index may provide little information beyond a more simple measure of the proportion of the population black.
The relationship of the magnitude of revascularization disparity to segregation was somewhat mixed. Using the Dissimilarity Index, we found that disparity in markets with medium and high hospital segregation was modestly lower (i.e., higher HRs), compared with markets with low hospital segregation. Results for residential Dissimilarity were slightly stronger. Moreover, this relationship persisted even after controlling for the admitting hospital, and in analyses limited to patients admitted to revascularization hospitals, suggesting that other environmental or social factors drive the relationship. If the uneven distribution of black and white patients across hospitals reflects populations choosing hospitals based on cultural identification and trust, utilization may be improved. Indeed, racial identity is an important determinant of individual actions for blacks (Philogene 2004
) and may facilitate or hinder health-seeking behavior depending on perceived concordance with providers in the black community. Moreover, cultural concordance may also impact patient compliance and outcomes (Saha et al. 1999
; Johnson et al. 2004
). Racially concentrated neighborhoods within segregated markets may also have greater social cohesion, leading to greater social support that facilitates access to health services (Wen, Browning, and Cagney 2003
), and the presence of autonomous institutions and social networks within segregated areas may mitigate the effects of racial mistrust and bias (Geronimus 2000
). Finally, we acknowledge the possibility that HRs in markets with high Dissimilarity may be overestimated, if our models do not adequately capture the need for revascularization among blacks in those communities.
In contrast to Dissimilarity, we found a modest increase in disparity (i.e., decrease in the relative HRs), as hospital Isolation increased, although this relationship was not statistically significant and disappeared entirely after controlling for the admitting hospital. Moreover, revascularization disparity was not related at all to residential isolation and was not evident using alternative market selection criteria. We hypothesized that Isolation would impact disparities through under-resourced hospitals, patient mistrust, and practice patterns of an isolated community. While these factors may limit the availability of revascularization in isolated communities, the relative disparity between blacks and whites remains consistent, regardless of isolation (i.e., if black patients are less likely to receive revascularization in isolated medical communities, so are white patients).
Our analysis required decisions about market selection criteria, patient sample selection, and segregation measurement. The limitations of these decisions, and possible variations, should be noted. First, the opportunity for segregation is lower in small markets (i.e., Dissimilarity across hospitals cannot exist in a market with only one hospital or with no black patients). Therefore, a minimum number of black patients and/or hospitals had to be identified. We selected markets with a minimum of 50 black patients and five hospitals, and conducted sensitivity analyses using four alternative market selection criteria (e.g., 25 black patients and five hospitals). Our conclusions were similar, regardless of market selection criteria.
Second, we excluded patients who did not reside in the same market as the hospital, which may affect the calculation of segregation for markets with large flows of patients into the market. However, segregation indices based on all patients were highly correlated to those we used (r>0.98 for both Isolation and Dissimilarity Indices).
Third, hospital services markets for acute medical conditions, such as AMI, may follow different patterns compared with hospitalizations for chronic conditions (e.g., CHF). In addition, this study focuses on elderly Medicare patients only; results based on all-payer data may differ.
Fourth, these analyses investigated only two dimensions of segregation—unevenness and isolation. Other dimensions include concentration (i.e., concentration of minorities within a spatial area) and centralization (i.e., centralization of minorities in large cities) (Massey and Denton 1988
). Finally, most segregation indices compare a single minority population to the majority (usually white) population, but multirace indices may be useful in markets with large proportions of other ethnic groups.
In summary, this study proposes a framework for studying pathways that create segregation of the health delivery system, as well as the link between segregation and disparities in utilization and outcomes of care. Our framework emphasizes pathways through which segregation may be both positively and negatively associated with health services and outcomes. We also evaluated the relationship between two dimensions of segregation and disparities in the use of revascularization—procedures for which substantial disparities have been documented. We found marked differences between the two dimensions of segregation and their relationship to revascularization disparities.
It is unlikely that the full racial and ethnic heterogeneity of health care markets can be summarized in a single number. Nevertheless, segregation indices, as overall measures of market structure, may have policy implications. First, if disparities are attributable to differential access to providers, then strategies to create parity in access may be beneficial. However, such efforts must consider the degree to which access of diverse populations depends on the community culture. Enhancing access for minorities goes beyond traditional competency training, and encompasses forces that create social cohesion, as well as distrust and fractionalization in the medical delivery system. Second, programs to encourage the use of high-quality hospitals, such as public dissemination of hospital performance measures, may be futile if black patients are limited in their choice of hospital due to social factors, choose certain hospitals because of cultural identification, or place a higher priority on perceived cultural competence than processes of care. Third, one must also consider the degree to which patient choice creates racial separation of health services. While the importance of preserving patient choice is generally recognized, U.S. history shows us that racially separate health delivery systems are not likely to be equal. Thus, segregation due to lack of options is undesirable; but segregation that reflects patient preferences may not be undesirable, as long as quality of care is maintained. Finally, the fact that significant segregation still exists in the health delivery system may warrant a civil rights approach to eliminating disparities. However, the underlying problem is not likely overt racial discrimination by health service organizations, but rather the failure to account for the needs of minority populations in health systems planning. Ultimately, the solution lies in a delivery system that respects the cultures of diverse populations, who often have diverse patterns of care, while addressing the health needs of those populations in a manner that is efficacious and constructive.