Original Article
Residential Racial Segregation and Mortality Among Black, White, and Hispanic Urban Breast Cancer Patients in Texas, 1995 to 2009 Sandi L. Pruitt, PhD, MPH1,2; Simon J. Craddock Lee, PhD, MPH1,2; Jasmin A. Tiro, PhD1,2; Lei Xuan, MS1; John M. Ruiz, PhD3; and Stephen Inrig, PhD1,4
BACKGROUND: The authors investigated whether residential segregation (the degree to which racial/ethnic groups live separately from one another in a geographic area) 1) was associated with mortality among urban women with breast cancer, 2) explained racial/ ethnic disparities in mortality, and 3) whether its association with mortality varied by race/ethnicity. METHODS: Using Texas Cancer Registry data, all-cause mortality and breast-cancer mortality were examined among 109,749 urban black, Hispanic, and white women aged 50 years who were diagnosed with breast cancer from 1995 to 2009. Racial (black) segregation and ethnic (Hispanic) segregation of patient’s neighborhoods were measured and were compared with the larger metropolitan statistical area using the location quotient measure. Shared frailty Cox proportional hazard models were used to nest patients within residential neighborhoods (census tract) and were controlled for race/ethnicity, age, diagnosis year, tumor stage, grade, histology, neighborhood poverty, and countylevel mammography availability. RESULTS: Greater black segregation and Hispanic segregation were adversely associated with cause-specific mortality and all-cause mortality. For example, in adjusted models, Hispanic segregation was associated with causespecific mortality (adjusted hazard ratio, 1.24; 95% confidence interval, 1.05-1.46). Compared with whites, blacks had higher mortality for both outcomes, whereas Hispanics demonstrated equivalent (cause-specific) or lower (all-cause) mortality. Segregation did not explain racial/ethnic disparities in mortality. Within each race/ethnicity strata, segregation was either adversely associated with mortality or was not significant. CONCLUSIONS: Among urban women with breast cancer in Texas, segregation has an independent, adverse association with mortality, and the effect of segregation varies by patient race/ethnicity. The novel application of a small-area measure of relative racial segregation should be examined in other cancer types with documented racial/ethnic disparities across varC 2015 American Cancer Society. ied geographic areas. Cancer 2015;121:1845-55. V KEYWORDS: health disparity, breast cancer, segregation, mortality, race, ethnicity.
INTRODUCTION Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death among women in the United States.1 Numerous studies have documented persistent racial/ethnic disparities in breast cancer mortality. Breast cancer disproportionately affects black women. Between 2004 and 2008, for example, US data demonstrate that black women experienced higher mortality rates (32.0 per 100,000) than white women (22.8 per 100,000) and Hispanic women (15.1 per 100,000).1 Many observers consider residential racial/ethnic segregation—that is, the degree to which groups live separately from 1 another in a geographic area2—to be a fundamental cause of racial/ethnic disparities in health in the United States, including cancer disparities.3 Residential racial segregation (hereafter “segregation”) may influence early breast cancer detection, cancer care delivery, and mortality. Extant research focuses on black-white segregation and has produced mixed findings. Thus, although some studies reported greater black-white segregation associated with adverse outcomes,4,5 others reported mixed effects depending on patient race,6,7 and still others reported no statistically significant associations whatsoever.8 Meanwhile, the influence of segregation on breast cancer outcomes among Hispanics remains largely unknown. Emerging evidence suggests that neighborhood effects observed in prior studies may not be generalizable to
Corresponding author: Sandi L. Pruitt, PhD, MPH, Department of Clinical Sciences, The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9169; Fax: (214) 648-3232; [email protected] 1 Department of Clinical Sciences, The University of Texas Southwestern Medical Center, Dallas, Texas; 2Harold C. Simmons Cancer Center, University of Texas Southwestern Medical Center Dallas, USA; 3Department of Psychology, University of North Texas, Denton, Texas; 4Department of History and Political Sciences, Mount St. Mary’s University, Los Angeles, California
We thank E. Scott Morris for assistance with census data. DOI: 10.1002/cncr.29282, Received: August 12, 2014; Revised: November 25, 2014; Accepted: December 17, 2014, Published online February 11, 2015 in Wiley Online Library (wileyonlinelibrary.com)
Cancer
June 1, 2015
1845
Original Article
Figure 1. Conceptual and measurement model of relationships between residential racial/ethnic segregation, individual race/ethnicity, and mortality for breast cancer patients.
Hispanics. In some studies to date, although not all,9 neighborhoods with a greater percentage of Hispanics were associated with improved cancer and other health outcomes.10-12 These mixed findings may stem from conceptual and methodological differences in measuring segregation.13 The 2 main measures of racial segregation across the health literature are: 1) large-area (eg, county, metropolitan statistical area [MSA]), formal segregation measures (eg, MSA dissimilarity index) and 2) neighborhood composition measures (eg, census tract percentage black) used as proxy measures of segregation.13 Conceptually, large-area segregation measures do not reflect the daily, lived experience of residents in a neighborhood. Likewise, neighborhood composition measures, although simple to calculate, implicitly assume that the composition of 1 neighborhood is independent of the spatial distribution of race in nearby neighborhoods and across the greater MSA. This assumption runs counter to conceptual definitions that explicitly define segregation as a spatial phenomenon and assertions that the most ideal measures of segregation are dispersion measures.14 Methodologically, large-area segregation measures are complex to calculate and interpret, requiring specialized software and training. A novel, recently introduced measure, the location quotient of residential racial segregation (LQ),15 over1846
comes many of these limitations. The LQ is a small-area measure of relative segregation calculated at the residential census tract level. It represents how much more segregated a patient’s neighborhood (census tract) is relative to the larger overall metropolitan area (MSA). Thus, the LQ is a ratio of 2 proportions; the proportion of population group m in the tract (numerator) and the proportion of population group m in the MSA (denominator). Calculating the LQ does not require specialized software or skills, and the LQ explicitly measures relative, not absolute, segregation. We incorporated this novel measure into a conceptual and measurement model of the correlations between segregation, individual race/ethnicity, and mortality for patients with breast cancer (Fig. 1). We developed the model and measures using existing conceptual frameworks and literature reviews on the health effects of segregation13,16-18 and breast cancer disparities19,20 as well as empirical evidence on segregation and breast cancer outcomes.4-8,21 Our model (Fig. 1) has 2 notable features. First, we explicitly define LQ as a measure of the relative segregation of the neighborhood compared with the segregation of the larger metropolitan area. Although the LQ incorporates absolute measures of racial/ethnic composition, it more closely mirrors conceptual definitions of segregation as a relative, contextual phenomenon best captured with Cancer
June 1, 2015
Segregation and Breast Cancer Mortality/Pruitt et al
measures of dispersion. Second, we posit that segregation directly affects breast cancer mortality5-7,13,17 and that patient race/ethnicity moderates the association between segregation and mortality. Prognostic factors (eg, age) and associated tumor factors (eg, stage) are also included in the model as important predictors of mortality (note that dotted lines in the figure indicate variables that were not measured in the current study). These include the multiple environmental and individual mechanisms through which segregation “gets under the skin” to adversely influence health outcomes. Although the mechanisms linking segregation and health have not been fully elucidated, they may include high unemployment, low income, deteriorated housing, poor-quality schools, and lower quality and poorer access to health care facilities.2,3,22,23 Using this model as a guide, we examined the association of residential racial segregation and mortality among black, Hispanic, and white urban patients who were diagnosed with breast cancer in Texas from 1995 to 2009. Specifically, we addressed the following questions: 1. Is greater segregation associated with higher mortality? 2. To what extent does segregation explain racial/ethnic disparities in mortality? 3. Does patient race/ethnicity moderate the association between segregation and mortality? MATERIALS AND METHODS Data and Sample
We obtained data from the Texas Cancer Registry (TCR), a North American Association of Central Cancer Registries gold-certified, population-based registry. We included adult women (aged 50 years) who had breast cancer diagnosed during the period 1995 to 2009 and who lived in an MSA. We selected women aged 50 years to minimize population heterogeneity, because the prognostic and demographic characteristics of younger women (aged
Residential Racial Segregation and Mortality Among Black, White, and Hispanic Urban Breast Cancer Patients in Texas, 1995 to 2009 Sandi L. Pruitt, PhD, MPH1,2; Simon J. Craddock Lee, PhD, MPH1,2; Jasmin A. Tiro, PhD1,2; Lei Xuan, MS1; John M. Ruiz, PhD3; and Stephen Inrig, PhD1,4
BACKGROUND: The authors investigated whether residential segregation (the degree to which racial/ethnic groups live separately from one another in a geographic area) 1) was associated with mortality among urban women with breast cancer, 2) explained racial/ ethnic disparities in mortality, and 3) whether its association with mortality varied by race/ethnicity. METHODS: Using Texas Cancer Registry data, all-cause mortality and breast-cancer mortality were examined among 109,749 urban black, Hispanic, and white women aged 50 years who were diagnosed with breast cancer from 1995 to 2009. Racial (black) segregation and ethnic (Hispanic) segregation of patient’s neighborhoods were measured and were compared with the larger metropolitan statistical area using the location quotient measure. Shared frailty Cox proportional hazard models were used to nest patients within residential neighborhoods (census tract) and were controlled for race/ethnicity, age, diagnosis year, tumor stage, grade, histology, neighborhood poverty, and countylevel mammography availability. RESULTS: Greater black segregation and Hispanic segregation were adversely associated with cause-specific mortality and all-cause mortality. For example, in adjusted models, Hispanic segregation was associated with causespecific mortality (adjusted hazard ratio, 1.24; 95% confidence interval, 1.05-1.46). Compared with whites, blacks had higher mortality for both outcomes, whereas Hispanics demonstrated equivalent (cause-specific) or lower (all-cause) mortality. Segregation did not explain racial/ethnic disparities in mortality. Within each race/ethnicity strata, segregation was either adversely associated with mortality or was not significant. CONCLUSIONS: Among urban women with breast cancer in Texas, segregation has an independent, adverse association with mortality, and the effect of segregation varies by patient race/ethnicity. The novel application of a small-area measure of relative racial segregation should be examined in other cancer types with documented racial/ethnic disparities across varC 2015 American Cancer Society. ied geographic areas. Cancer 2015;121:1845-55. V KEYWORDS: health disparity, breast cancer, segregation, mortality, race, ethnicity.
INTRODUCTION Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death among women in the United States.1 Numerous studies have documented persistent racial/ethnic disparities in breast cancer mortality. Breast cancer disproportionately affects black women. Between 2004 and 2008, for example, US data demonstrate that black women experienced higher mortality rates (32.0 per 100,000) than white women (22.8 per 100,000) and Hispanic women (15.1 per 100,000).1 Many observers consider residential racial/ethnic segregation—that is, the degree to which groups live separately from 1 another in a geographic area2—to be a fundamental cause of racial/ethnic disparities in health in the United States, including cancer disparities.3 Residential racial segregation (hereafter “segregation”) may influence early breast cancer detection, cancer care delivery, and mortality. Extant research focuses on black-white segregation and has produced mixed findings. Thus, although some studies reported greater black-white segregation associated with adverse outcomes,4,5 others reported mixed effects depending on patient race,6,7 and still others reported no statistically significant associations whatsoever.8 Meanwhile, the influence of segregation on breast cancer outcomes among Hispanics remains largely unknown. Emerging evidence suggests that neighborhood effects observed in prior studies may not be generalizable to
Corresponding author: Sandi L. Pruitt, PhD, MPH, Department of Clinical Sciences, The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9169; Fax: (214) 648-3232; [email protected] 1 Department of Clinical Sciences, The University of Texas Southwestern Medical Center, Dallas, Texas; 2Harold C. Simmons Cancer Center, University of Texas Southwestern Medical Center Dallas, USA; 3Department of Psychology, University of North Texas, Denton, Texas; 4Department of History and Political Sciences, Mount St. Mary’s University, Los Angeles, California
We thank E. Scott Morris for assistance with census data. DOI: 10.1002/cncr.29282, Received: August 12, 2014; Revised: November 25, 2014; Accepted: December 17, 2014, Published online February 11, 2015 in Wiley Online Library (wileyonlinelibrary.com)
Cancer
June 1, 2015
1845
Original Article
Figure 1. Conceptual and measurement model of relationships between residential racial/ethnic segregation, individual race/ethnicity, and mortality for breast cancer patients.
Hispanics. In some studies to date, although not all,9 neighborhoods with a greater percentage of Hispanics were associated with improved cancer and other health outcomes.10-12 These mixed findings may stem from conceptual and methodological differences in measuring segregation.13 The 2 main measures of racial segregation across the health literature are: 1) large-area (eg, county, metropolitan statistical area [MSA]), formal segregation measures (eg, MSA dissimilarity index) and 2) neighborhood composition measures (eg, census tract percentage black) used as proxy measures of segregation.13 Conceptually, large-area segregation measures do not reflect the daily, lived experience of residents in a neighborhood. Likewise, neighborhood composition measures, although simple to calculate, implicitly assume that the composition of 1 neighborhood is independent of the spatial distribution of race in nearby neighborhoods and across the greater MSA. This assumption runs counter to conceptual definitions that explicitly define segregation as a spatial phenomenon and assertions that the most ideal measures of segregation are dispersion measures.14 Methodologically, large-area segregation measures are complex to calculate and interpret, requiring specialized software and training. A novel, recently introduced measure, the location quotient of residential racial segregation (LQ),15 over1846
comes many of these limitations. The LQ is a small-area measure of relative segregation calculated at the residential census tract level. It represents how much more segregated a patient’s neighborhood (census tract) is relative to the larger overall metropolitan area (MSA). Thus, the LQ is a ratio of 2 proportions; the proportion of population group m in the tract (numerator) and the proportion of population group m in the MSA (denominator). Calculating the LQ does not require specialized software or skills, and the LQ explicitly measures relative, not absolute, segregation. We incorporated this novel measure into a conceptual and measurement model of the correlations between segregation, individual race/ethnicity, and mortality for patients with breast cancer (Fig. 1). We developed the model and measures using existing conceptual frameworks and literature reviews on the health effects of segregation13,16-18 and breast cancer disparities19,20 as well as empirical evidence on segregation and breast cancer outcomes.4-8,21 Our model (Fig. 1) has 2 notable features. First, we explicitly define LQ as a measure of the relative segregation of the neighborhood compared with the segregation of the larger metropolitan area. Although the LQ incorporates absolute measures of racial/ethnic composition, it more closely mirrors conceptual definitions of segregation as a relative, contextual phenomenon best captured with Cancer
June 1, 2015
Segregation and Breast Cancer Mortality/Pruitt et al
measures of dispersion. Second, we posit that segregation directly affects breast cancer mortality5-7,13,17 and that patient race/ethnicity moderates the association between segregation and mortality. Prognostic factors (eg, age) and associated tumor factors (eg, stage) are also included in the model as important predictors of mortality (note that dotted lines in the figure indicate variables that were not measured in the current study). These include the multiple environmental and individual mechanisms through which segregation “gets under the skin” to adversely influence health outcomes. Although the mechanisms linking segregation and health have not been fully elucidated, they may include high unemployment, low income, deteriorated housing, poor-quality schools, and lower quality and poorer access to health care facilities.2,3,22,23 Using this model as a guide, we examined the association of residential racial segregation and mortality among black, Hispanic, and white urban patients who were diagnosed with breast cancer in Texas from 1995 to 2009. Specifically, we addressed the following questions: 1. Is greater segregation associated with higher mortality? 2. To what extent does segregation explain racial/ethnic disparities in mortality? 3. Does patient race/ethnicity moderate the association between segregation and mortality? MATERIALS AND METHODS Data and Sample
We obtained data from the Texas Cancer Registry (TCR), a North American Association of Central Cancer Registries gold-certified, population-based registry. We included adult women (aged 50 years) who had breast cancer diagnosed during the period 1995 to 2009 and who lived in an MSA. We selected women aged 50 years to minimize population heterogeneity, because the prognostic and demographic characteristics of younger women (aged
