Spatial Cluster Analysis of the Social Determinants of Health and Fatal Crashes Involving US Geriatric and Non-Geriatric Road Users

Social determinants of health (SDoH) are nonmedical factors impacting health outcomes. We evaluated the relationship between the county-level measure of SDoH and county-level fatal crash counts among geriatric and non-geriatric road users. We pooled data from the Fatality Analysis Reporting System and limited our analyses to the 3108 contiguous US counties. The outcome measures were county-level fatal crash counts involving (1) geriatric (65 years and older), (2) non-geriatric, and (3) all road users. The predictor variable was the multidimensional deprivation index (MDI), a composite measure of SDoH, measured as a three-level categorical variable defined as very highly deprived, highly deprived, and average-to-low deprived. We performed a Bayesian spatial Poisson regression analysis using integrated nested Laplace approximations and reported the adjusted crash fatality rate ratios (plus 95% credible intervals (CrI)). The median (Q1, Q3) standardized mortality rate ratios among geriatric and non-geriatric road users were 1.3 (0.6, 2.5) and 1.6 (0.9, 2.7), respectively. Counties classified as very highly deprived had 23% (95% CrI: 1.10–1.38) and 20% (95% CI: 1.08–1.32) increased geriatric and non-geriatric fatality crash rate ratios. In conclusion, improving county-level SDoH may reduce the county-level fatal rate ratios equally among geriatric and non-geriatric road users.