MethodologyIdentification of racial disparities in breast cancer mortality : does scale matter ?

Background: This paper investigates the impact of geographic scale (census tract, zip code, and county) on the detection of disparities in breast cancer mortality among three ethnic groups in Texas (period 1995-2005). Racial disparities were quantified using both relative (RR) and absolute (RD) statistics that account for the population size and correct for unreliable rates typically observed for minority groups and smaller geographic units. Results were then correlated with socio-economic status measured by the percentage of habitants living below the poverty level. Results: African-American and Hispanic women generally experience higher mortality than White non-Hispanics, and these differences are especially significant in the southeast metropolitan areas and southwest border of Texas. The proportion and location of significant racial disparities however changed depending on the type of statistic (RR versus RD) and the geographic level. The largest proportion of significant results was observed for the RD statistic and census tract data. Geographic regions with significant racial disparities for African-Americans and Hispanics frequently had a poverty rate above 10.00%. Conclusions: This study investigates both relative and absolute racial disparities in breast cancer mortality between White non-Hispanic and African-American/Hispanic women at the census tract, zip code and county levels. Analysis at the census tract level generally led to a larger proportion of geographical units experiencing significantly higher mortality rates for minority groups, although results varied depending on the use of the relative versus absolute statistics. Additional research is needed before general conclusions can be formulated regarding the choice of optimal geographic regions for the detection of racial disparities. Background Breast cancer is the most common cancer among women and accounts alone for 31% of diagnosed cases in the United States [1]. The lifetime risk for women to develop breast cancer has nearly tripled in the last sixty years from 1 in 22 to 1 in 8 [2]. However, all persons are not equal when faced with this disease: different racial and socio-economic groups display striking disparities across regions with respect to late-stage diagnosis and mortality rates of breast cancer [3-5]. From 1998 to 2002, breast cancer mortality among African-American women was 50% higher than for white women: 36.0 deaths versus 24.4 deaths per 100,000 women, respectively [6]. AfricanAmericans living in counties with more than 20% of the population below the poverty line had more than 6% higher mortality in breast cancer than those living in counties with less than 10% poverty line [7]. Geography is a critical factor that drives reported racial/ethnic and socioeconomic disparities through a large adverse impact on the level and quality of received health care in that African-Americans and Hispanics tend to live in different areas than the White non-Hispanic population. Hispanics disproportionally account for 56% of 3.8 millions Texans living in poverty in contrast to 17% African-Americans and 24% White non-Hispanics [8]. Health disparities related to race and socioeconomic status are particularly important in a large state like Texas. Out of 12 million female people in Texas, 15,132 women were diagnosed with breast cancer in 2008; and 18.4 percent of them (about 2,780) were expected to die from the disease [9]. The massive burden of breast cancer caused by the disproportionate representation of African-Americans and Hispanics in Texas, as * Correspondence: jt1277@txstate.edu 1 Texas Center for Geographic Information Science, Department of Geography, Texas State University-San Marcos, 601 University Drive, San Marcos, Texas,