Spatially continuous local rate modeling for communication in public health: a practical approach.

A primary function of Environmental Public Health Tracking is the communication of spatial trends of diseases. Traditional (choropleth) approaches to disease mapping}?> have difficulty conveying intuitive understandings of the spatial continuity of disease risk, rate calculations in rural areas, and degrees of statistical significance. A spatial loess function can be utilized to depict continuous variations in preterm birth risk for the state of California on the basis of a 3-year birth cohort. Results from this function were graphically depicted and incorporated into a Web mapping service to maximize public accessibility. The function was evaluated as a tool for communication by considering its intuitive interpretation and comparing information derived from the function with that, which would be derived from a choropleth map using the same data. In general, the loess function was able to generate risk information for a variety of both urban and rural settings. Although richer in detail, this information was mostly consistent with that which would come from choropleth maps. Occasionally, information from the loess function stood in contradiction to the choropleth mapping procedure; however; we enumerate these occasions and discuss ways to maximize the consistency of the loess function with intuitive understandings of disease risk.