City living, healthy living? : the relationship between density and health in U.S. counties and cities

In this honors thesis I investigate the relationship between urbanicity and health in the United States. I review the literature of place-based effects on health and present the differences between cities and counties as the primary unit of analysis. Using t-tests I show that cities and counties describe different populations and, consequently, that county data cannot be used to describe city populations. I also investigate the associations between density and coronary heart disease mortality, breast cancer mortality and diabetes mortality after adjusting for socioeconomic status, demographics and health care availability using multiple regression. I use aggregate county data for 3,103 U.S. counties and aggregate city data for the 54 largest U.S. cities to examine the incidence of these three health outcomes across a large range of densities, transformed to log density. All three health outcomes have highly significant nonlinear relationships with log density. Coronary heart disease mortality is associated with density even after controlling for a range of socioeconomic, demographic and health care-related factors. This relationship is highly nonlinear and has at least two inflection points (F (11, 3087) = 188.98; RMSE = 73.12; p\u3c 0.0001). Compared to a similar model without density, density explains an additional 7 percent of the variance. Breast cancer mortality is also highly associated with density after controlling for socioeconomic, demographic and care-related factors (F (11,2706) = 110.40; RMSE = 10.55; p\u3c 0.0001) and is also highly nonlinear. In this model, density explains about 13 percent of additional variance. Diabetes incidence is also related to density (F (10, 2701)= 96.67; RMSE = 2.38; p\u3c 0.0001) and density explains about 2 percent of additional variance. Both the breast cancer mortality and CHD mortality models show two inflection points in the relationship with density, including a precipitous drop in mortality incidence between 30 people/mile2 and 100 people/mile2. The association between these two health outcomes and density diminishes at higher densities (\u3e1,000 people/mile2). This relationship is mirrored in the city data; the variation in density between large U.S. cities has no consistent relationship with either heart disease mortality or breast cancer mortality. Density is an important measure of urbanicity and may be one variable to describe how the social, physical and service environment shapes health; the highly nonlinear relationships seen here merit further investigation and understanding