Firearm homicides occur less frequently in US states with more firearm control laws. However, firearms are easily transported across state lines, and laws in one location may affect firearm violence in another. A research team composed of PISC Scholars, led by PISC Past Trainee, Christopher Morrison, examined associations between within-state firearm laws and firearm homicide while accounting for interference from laws in other nearby states. Other PISC affiliated researchers involved include PISC Senior Scholar, Elinore Kaufman, MD, MSHP, International Scholar and External Advisory Board Member, David Humphreys, PhD, along with Senior Author and PISC Director Douglas Weibe, PhD.
There were 172,726 firearm homicides in the included counties over the 15 years. States had between 3 and 100 firearm laws. Within-state firearm laws and interstate firearm laws were independently associated with fewer firearm homicides, and associations for within-state laws were strongest where interstate laws were weakest. Additional firearm laws are associated with fewer firearm homicides both within the states where the laws are enacted and elsewhere in the US. Interference from interstate firearm laws may bias associations for studies of within-state laws and firearm homicide.