Catchment Area Analysis Using Generalized Additive Models

A catchment area is the geographic area and population from which a health service center draws patients. Defining a catchment area allows the service center to describe its primary patient population and assess how well it meets the needs of patients within the catchment area. A catchment area definition is required for cancer centers applying for NCI-designated Cancer Center status. In this research, we estimated diagnosis catchment areas for the Massey Cancer Center (MCC) at Virginia Commonwealth University using a Generalized Additive Model (GAM) framework. We estimated diagnosis catchment areas for all cancers based on individual-level Virginia state cancer registry data. We used a GAM with a spatial smoother to model the residual log odds of being diagnosed with cancer at MCC after accounting for several covariates, including age, race, ethnicity, gender, and health insurance type. In addition, we used a Generalized Additive Mixed Model (GAMM) to account for multiple cancer diagnoses for the same patient. To define catchment areas, we identified the geographic areas with statistically significant residual log odds of being diagnosed for cancer at MCC. The diagnosis catchment area for MCC estimated from the GAM included 58 counties. Characteristics associated with increased odds of being diagnosed with cancer at MCC included black race, Hispanic ethnicity, younger age, no health insurance, and Medicaid health insurance.