Association between Firearm Laws and Homicide in Urban Counties

Abstract

Laws related to the sale, use, and carrying of firearms have been associated with differences in firearm homicide rates at the state level. Right-to-carry (RTC) and stand your ground (SYG) laws are associated with increases in firearm homicide; permit-to-purchase (PTP) laws and those prohibiting individuals convicted of violent misdemeanors (VM) have been associated with decreases in firearm homicide. Evidence for the effect of comprehensive background checks (CBC) not tied to PTP is inconclusive. Because firearm homicide tends to concentrate in urban areas, this study was designed to test the effects of firearm laws on homicide in large, urban U.S. counties. We conducted a longitudinal study using an interrupted time series design to evaluate the effect of firearm laws on homicide in large, urban U.S. counties from 1984 to 2015 (N = 136). We used mixed effects Poisson regression models with random intercepts for counties and year fixed effects to account for national trends. Models also included county and state characteristics associated with violence. Homicide was stratified by firearm versus all other methods to test for specificity of the laws' effects. PTP laws were associated with a 14% reduction in firearm homicide in large, urban counties (IRR = 0.86, 95% CI 0.82-0.90). CBC-only, SYG, RTC, and VM laws were all associated with increases in firearm homicide. None of the laws were associated with differences in non-firearm homicide rates. These findings are consistent with prior research at the state level showing PTP laws are associated with decreased firearm homicide. Testing the effects of PTP laws specifically in large, urban counties strengthens available evidence by isolating the effects in the geographic locations in which firearm homicides concentrate.

Evidence concerning the regulation of firearms design, sale, and carrying on fatal mass shootings in the United States

“…Some licensing laws also require gun safety training, and a few provide officials the ability to use their discretion to deny an applicant if there is good reason to believe he or she might be dangerous (e.g., some history of violence). Rigorous studies of the impact of state CBC laws have not shown that these laws reduce homicides (Castillo‐Carniglia et al., ; Kagawa et al., ; Zeoli et al., ); however, there has been consistent evidence that licensing laws reduce homicides (Crifasi et al., ; Hasegawa, Webster, & Small, ; Rudolph, Stuart, Vernick, & Webster, ) and suicides (Crifasi, Meyers, Vernick, & Webster, ). Licensing laws could potentially suppress fatal mass shootings, but there are no rigorous studies examining this question.…”

The Impact of State Firearm Laws on Homicide Rates in Suburban and Rural Areas Compared to Large Cities in the United States, 1991‐2016

“…12,14,15 Crifasi and associates studied the relationship between 5 state firearm laws and homicide rates in heavily populated US counties during the period 1984-2015. 12 They found that laws requiring a permit to purchase firearms were associated with an 11% reduction in firearm homicide in these urban counties. Right-to-carry laws, stand your ground laws, and violent misdemeanor prohibitions were associated with increases in firearm homicides of 7%, 8%, and 24%, respectively.…”

“…Most of the public health literature on homicide classifies urbanicity at the county level using coding schemes developed by CDC or US Department of Agriculture (USDA) ( Table A1; available online only). [5][6][7][8][9][10][11][12] Isserman highlights a problem (which he terms the "county trap") of classifying urbanicity based on counties because these designations capture integration rather than separation. 24 Research that uses CDC or USDA distinctions are classifying many counties as urban because they are tied to metropolitan areas even if the qualities of the areas making up the county being classified are decidedly nonurban on their own.…”

“…We lagged the state laws by 1 year so that the impact of these laws was assessed starting in the first full year they were in effect, not when the law was enacted, following the approach of Lott and Mustard. 36 Based on previous research, we selected 6 laws for analysis: (1) universal background checks for all guns at point-of-sale 37,38 ; (2) permits required to purchase or possess any firearm 12,39,40 ; (3) ban on firearm possession by people convicted of a violent misdemeanor 41,42 ; (4) stringent "may issue" laws ("may issue" laws that require the concealed carry permit applicant to make a heightened showing of having a need to carry a concealed firearm) 12,41,43,44 ; (5) "stand your ground" laws 45,46 ; and (6) ban on gun trafficking 47 (Table 2).…”

“…An important contribution of the present study is the use of cities, rather than counties, as the basis for disaggregation of homicide rates. Most of the public health literature on homicide classifies urbanicity at the county level using coding schemes developed by CDC or US Department of Agriculture (USDA) (; available online only) . Isserman highlights a problem (which he terms the “county trap”) of classifying urbanicity based on counties because these designations capture integration rather than separation .…”