Do Seat Belt Laws Still Work? Replication and Re-Evaluation of Recent Evidence

Abstract

Recent work suggests that mandatory seatbelt laws are associated with lower motor vehicle accident mortality, but it is unclear whether this is due to increased enforcement. We study this association using 2001-2010 US data on traffic fatalities among individuals ages 10 and over and we test the robustness of unstated assumptions by replicating and extending prior work. Using Poisson regression adjusted for state-level traffic safety policies (seat belt laws, blood alcohol laws, speed limits), miles traveled, and median income, we replicate the covariate-adjusted association seen in prior work (Rate Ratio [RR]=0.80, 95%CI 0.74,0.87). Further adjustment for state and time fixed effects showed no evidence of a causal effect (RR=1.00, 95%CI 0.95,1.06). We find little evidence that seatbelt laws reduce traffic fatalities, and prior work was confounded by general improvements in other environmental determinants of motor vehicle accident mortality. Replications studies have the potential to increase the integrity of research findings.