Historic redlining, social mobility, and firearm violence.

Background: Much of the recorded medical literature focuses on individual-level factors that contribute to firearm violence. Recently, studies have highlighted higher incidence of firearm violence in historically redlined and marginalized areas, but few have gone on to study the downstream associations causing these differences. This study aims to understand the effects of historic redlining and current income mobility on firearm violence.

Methods: Using a retrospective cross-sectional design, shooting incidents were spatially joined with redlining vector files and linked to income mobility data (how much a child makes in adulthood). Participants included all assault and homicide incidents involving a firearm in the city of Boston, between 2016 and 2019. The exposure of interest was redlining designation as outlined by the Home Owner's Loan Corporation (HOLC) in the 1930s and income mobility, stratified by race, defined as the income of a child in their 30s compared with where they grew up (census tract level). The outcome measured was shooting rate per census block.

Results: We find that increases in Black income mobility (BIM) and White income mobility (WIM) are associated with significant decreases in rates of firearm incidents in all HOLC designations; however, there is a larger decrease with increasing BIM (relative risk, 0.47 per unit increase in BIM [95% confidence interval, 0.35-0.64]; relative risk, 0.81 per unit increase in WIM [95% confidence interval, 0.71-0.93]). Plotting predicted rates of firearm violence in each HOLC designation at different levels of BIM, there were no significant differences in shooting rates between historically harmful and beneficial classifications above $50,000 of BIM. Despite level of WIM, there were continued disparities between harmful and beneficial HOLC classification.

Conclusion: These findings highlight the importance of structural racism in the form of redlining and discriminatory housing policies, and the preclusion from economic mobility therein, on the incidence of firearm violence today.

Level Of Evidence: Prognostic and Epidemiological; Level IV.