Disparities of Colorectal Cancer Survival in Texas
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Disparities in colorectal cancer (CRC) outcomes in terms of race/ethnicity, socioeconomic status (SES), and geographic location have been widely documented in the United States. However, the mechanism of how different factors influence the disparities remains poorly understood. Previous studies of CRC disparity are limited because (1) they seldom evaluated the joint influence of multiple factors on CRC outcomes, (2) few US studies have investigated the association between potential spatial access to CRC services and CRC outcomes, and (3) the effects of spatial autocorrelation, the small number problem, and the ecological fallacy on analysis results were not fully accounted for. These limitations prevent researchers and health professionals from more accurately understanding the causes of disparities and effectively designing intervention programs. Taking advantage of Geographic Information Science and statistical methods, this dissertation investigates disparities of CRC stage at diagnosis and CRC-specific survival in Texas during the period from 1995 to 2003. Specifically, it proposes a relative spatial access assessment approach to estimate potential spatial access to CRC prevention and treatment services in Texas (Chapter 4), adopts the generalized equation estimating logistic regression and the adaptive spatial filtering method to evaluate the collective influence of race/ethnicity, SES, geographic location, and potential spatial access to CRC prevention services on CRC stage at diagnosis (Chapter 5), and employs the Kaplan-Meier estimator, the Cox proportional hazard regression, and the spatial scan statistic to uncover the complex disparities of CRC survival (Chapter 6). It is shown that the proposed spatial access approach could effectively overcome the uncertainty problem of gravity-based spatial access models. There were obvious differences in potential spatial access to CRC services by socio-demographic and geographic factors. The investigations into the continuum of CRC reveal systematic disparities in CRC stage at diagnosis and CRC-specific survival by race/ethnicity, SES, and geographic location, with disproportionately unfavorable burdens on non-Hispanic blacks, Hispanics, people from low SES areas, and individuals from specific geographic areas. Potential spatial access to CRC services was found to be associated with CRC stage at diagnosis across the whole state and with CRC-specific survival for non-urban areas. However, the impact of the potential spatial access was minor compared to those of race/ethnicity and SES. This dissertation provides new insights about how CRC disparities accumulate from the diagnosis to mortality in a large and diverse population. The results are useful for CRC disparity elimination and cancer resource allocation in Texas. In addition, this dissertation demonstrates the usefulness of a comprehensive framework of utilizing spatial analysis techniques to complement social epidemiological studies of health disparity.