The lagged effect of state gun laws on the reduction of state-level firearm homicide mortality in the United States from 1999 to 2017

Abstract Objectives Gun violence is a pressing concern in the United States, where many laws targeting gun violence vary across states and localities. Studies have investigated the association between gun laws and gun violence, but not many focus on the role of time, which is critical for implementation. This study aims to determine the lagged association of gun laws with firearm homicide mortality to better understand the impacts of state gun laws over time. Study design The design of this study is a longitudinal study. Methods This study applied the distributed lag non-linear model to assess the lagged association between firearm homicide mortality and the number of gun law provisions at the state level from 1999 to 2017. State gun law provisions were analyzed in aggregate and also across five groups of regulations. All estimates were transformed into relative risks (RRs). Results Regarding all state gun laws, regardless of how many gun law provisions were on the books in any year, a significantly reduced RR of firearm homicide mortality was not observed until 7 years later. Among the five regulation groups, a significant RR less than 1 was more likely to happen in longer lags ≥5. The lowest significant RR = 0.24 (95% confidence interval = 0.15, 0.39) was observed in the gun types, components, and trafficking group at lag 8. All regulation groups had an overall impact to reduce significantly the RR of firearm homicide mortality with more gun law provisions, except for the dealer regulation group. Conclusions State gun law provisions appear to impact firearm homicide mortality differently over time. This emphasizes the centrality of enforcement. Firearm policy researchers need to consider how specific gun laws are implemented over time to help inform law-based interventions.