Design of a location-based case-control study of built-environment risk factors for pedestrian fatalities in the United States

Abstract

The location-based case-control design is a useful approach for studies in which the exposures of interest are aspects of the environment around the location of a health event, such as a pedestrian fatality. In this design, locations are the unit of analysis, an enumerated cohort of locations is followed through time for the health events of interest, and a case-control study of locations is nested within the cohort. Locations where events occurred (case locations) are compared with matched locations where these events did not occur (control locations). We describe the application of this design to the issue of pedestrian fatalities, using a cohort of 9 612 698 intersections, 17 737 728 road segments, and 222 318 entrance/exit ramp segments that existed in 2017 across all 384 US metropolitan statistical areas. This cohort of locations was followed up from January 1, 2017, to December 31, 2018, for pedestrian fatalities, using the National Highway Traffic Safety Administration Fatality Analysis Reporting System. In total, 10 587 fatalities were identified as having occurred in cohort locations, and 21 174 matched control locations were selected using incidence density sampling. Geographic information systems, spatially linked administrative data sets, and virtual neighborhood audits via Google Street View are underway to characterize study locations.