Interactive associations of cannabis and alcohol outlet densities with assault injuries in California: a spatiotemporal analysis

Recreational cannabis outlets may influence rates of interpersonal violence, but research has yielded inconsistent findings. Modification by alcohol outlet density may help explain inconsistencies. We estimated the impacts of recreational cannabis outlets on neighborhood-level assault injury rates in California and evaluated whether alcohol outlet density moderated these associations. We applied Bayesian spatiotemporal analyses to ZIP code-level statewide data on alcohol outlets, recreational cannabis outlets, and injuries and deaths due to firearm and nonfirearm assault, from 2017 to 2019, accounting for confounders and spatial autocorrelation. Using the model posteriors, we estimated parameters corresponding to hypothetical shifts in outlet densities, overall and by age, sex, and race/ethnicity. If recreational cannabis outlets were never introduced, we estimated that nonfirearm assault injuries would have been 1.63 per 100 000 lower (95% CI, -3.08 to 0.01), but we observed no association with firearm assault injuries (risk difference [RD] per 100 000: -0.07; 95% CI, -0.34 to 0.21). These associations did not depend on alcohol outlet density, but a hypothetical 20% reduction in alcohol outlet densities was associated with fewer firearm (RD per 100 000: -1.89; 95% CI, -0.46 to 0.09) and nonfirearm (RD per 100 000: -5.67; 95% CI, -7.44 to -3.95) assault injuries. The introduction of recreational cannabis outlets may have contributed to a small increase in nonfirearm assault injuries.