Homicide Deaths Among Adult Cohabitants of Handgun Owners in California, 2004 to 2016

Although personal protection is a major motivation for purchasing firearms, existing studies suggest that people living in homes with firearms have higher risks for dying by homicide. Distribution of those risks among household members is poorly understood.To estimate the association between living with a lawful handgun owner and risk for homicide victimization.This retrospective cohort study followed 17.6 million adult residents of California for up to 12 years 2 months (18 October 2004 through 31 December 2016). Cohort members did not own handguns, but some started residing with lawful handgun owners during follow-up.California.17 569 096 voter registrants aged 21 years or older.Homicide (overall, by firearm, and by other methods) and homicide occurring in the victim's home.Of 595 448 cohort members who commenced residing with handgun owners, two thirds were women. A total of 737 012 cohort members died; 2293 died by homicide. Overall rates of homicide were more than twice as high among cohabitants of handgun owners than among cohabitants of nonowners (adjusted hazard ratio, 2.33 [95% CI, 1.78 to 3.05]). These elevated rates were driven largely by higher rates of homicide by firearm (adjusted hazard ratio, 2.83 [CI, 2.05 to 3.91]). Among homicides occurring at home, cohabitants of owners had sevenfold higher rates of being fatally shot by a spouse or intimate partner (adjusted hazard ratio, 7.16 [CI, 4.04 to 12.69]); 84% of these victims were female.Some cohort members classified as unexposed may have lived in homes with handguns. Residents of homes with and without handguns may have differed on unobserved traits associated with homicide risk.Living with a handgun owner is associated with substantially elevated risk for dying by homicide. Women are disproportionately affected.The National Collaborative on Gun Violence Research, the Fund for a Safer Future, the Joyce Foundation, Stanford Law School, and the Stanford University School of Medicine.