Simulating the bounds of plausibility: Estimating the impact of high-risk versus population-based approaches to prevent firearm injury

Social Vulnerability and Firearm Violence: Geospatial Analysis of 5 US Cities

BACKGROUND

Firearm violence is now endemic to certain US neighborhoods. Understanding factors that impact a neighborhood's susceptibility to firearm violence is crucial for prevention. Using a nationally standardized measure to characterize community-level firearm violence risk has not been broadly studied but could enhance prevention efforts. Thus, we sought to examine the association between firearm violence and the social, structural, and geospatial determinants of health, as defined by the Social Vulnerability Index (SVI).

STUDY DESIGN

In this cross-sectional study, we merged 2018 SVI data on census tract with shooting incidents between 2015 and 2021 from Baltimore, Chicago, Los Angeles, New York City, and Philadelphia. We used negative binomial regression to associate the SVI with shooting incidents per 1,000 people in a census tract. Moran's I statistics and spatial lag models were used for geospatial analysis.

RESULTS

We evaluated 71,296 shooting incidents across 4,415 census tracts. Fifty-five percent of shootings occurred in 9.4% of census tracts. In all cities combined, a decile rise in SVI resulted in a 37% increase in shooting incidents (p < 0.001). A similar relationship existed in each city: 30% increase in Baltimore (p < 0.001), 50% in Chicago (p < 0.001), 28% in Los Angeles (p < 0.001), 34% in New York City (p < 0.001), and 41% in Philadelphia (p < 0.001). Shootings were highly clustered within the most vulnerable neighborhoods.

CONCLUSIONS

In 5 major US cities, firearm violence was concentrated in neighborhoods with high social vulnerability. A tool such as the SVI could be used to inform prevention efforts by directing resources to communities most in need and identifying factors on which to focus these programs and policies.

Neighborhood segregation, tree cover and firearm violence in 6 U.S. cities, 2015-2020

Neighborhood segregation by race and income is a structural determinant of firearm violence. Addressing green space deficits in segregated neighborhoods is a promising prevention strategy. This study assessed the potential for reducing firearm violence disparities by increasing access to tree cover. Units of analysis were census tracts in six U.S. cities (Baltimore, MD; Philadelphia, PA; Richmond, VA; Syracuse, NY; Washington, DC; Wilmington, DE). We measured segregation using the index of concentration at the extremes (ICE) for race-income. We calculated proportion tree cover based on 2013-2014 imagery. Outcomes were 2015-2020 fatal and non-fatal shootings from the Gun Violence Archive. We modeled firearm violence as a function of ICE, tree cover, and covariates representing the social and built environment. Next, we simulated possible effects of "tree equity" programs, i.e., raising tract-level tree cover to a specified baseline level. In our fully-adjusted model, higher privilege on the ICE measure (1 standard deviation, SD) was associated with a 42% reduction in shootings (incidence rate ratio (IRR) = 0.58, 95% CI [0.54 0.62], p < 0.001). A 1-SD increase in tree cover was associated with a 9% reduction (IRR = 0.91, 95% CI [0.86, 0.97], p < 0.01). Simulated achievement of 40% baseline tree cover was associated with reductions in firearm violence, with the largest reductions in highly-deprived neighborhoods. Advancing tree equity would not disrupt the fundamental causes of racial disparities in firearm violence exposure, but may have the potential to help mitigate those disparities.