Studies Violence Prevention Research Program (VPRP) found that comprehensive background check policies led to increased background checks in Delaware, but not in Colorado or Washington. Non-compliance with the policy may explain the lack of an increase in the latter two states. Universal background check laws were associated with a 14.9% reduction in overall homicides, according to a 2019 study by medical researchers including
Michael Siegel of the
Boston University School of Public Health and
David Hemenway of the
Harvard T.H. Chan School of Public Health published by the
Journal of General Internal Medicine. The study authors wrote that "further research is necessary to determine whether these associations are causal ones". An October 2018 study conducted by the VPRP at
UC Davis and the Center for Gun Policy and Research at Johns Hopkins Bloomberg School of Public Health found no change in firearm homicide or suicide rates in the ten years following California's 1991 implementation of comprehensive background checks. The study's control group used firearm and non-firearm mortality data for 32 states that did not implement major firearm policies during the period from 1981 to 2000. In the study period, firearm suicide rates were 10.9% lower in California but a similar decrease in non-firearm suicide was also observed. The study found no net difference between firearm-related homicide rates before and during the study period. The study authors identified a number of possible reasons for the
null finding, including inadequate reporting of criminal records or other disqualifying information to background-check databases (especially pre-2000); a failure by sellers to conduct the background check as required by law; and the small number of persons affected by the California law. A study published in July 2018 found no
association between firearm homicide and suicide rates and the repeal of comprehensive background check laws in two states. The study compared rates from
synthetic control groups to rates in Indiana from 1981 to 2008 and in Tennessee from 1994 to 2008. Rates from the two states' study periods were within the range of
natural variability. The study also concluded that in order to understand whether comprehensive background checks generally reduce firearm deaths, more evidence from other states is needed. A study published in June 2018 in the
Journal of Urban Health by authors affiliated with the VPRP at
UC Davis and the Center for Gun Policy and Research at
Johns Hopkins Bloomberg School of Public Health found comprehensive background check (CBC) laws not tied to a permit-to-purchase law were associated with an increase in firearm homicide rates but not non-firearm homicide rates. The authors of the study noted, however, that they have "identified no plausible theory to explain how requiring a prospective firearm purchaser to undergo a background check would result in increased homicide rates." Additionally, the researchers' projection of a federally implemented universal background check policy predicted that national firearm mortality could drop from 10.35 deaths per 100,000 people to 4.46 deaths per 100,000 people. A 2014 study published in the
Journal of Urban Health found that the 2007 repeal of a "permit-to-purchase" handgun law in
Missouri (including the repeal of a background-check requirement) was associated with a 23% increase in the firearm homicide rate and a 15% increase in the murder rate, translating "to increases of between 55 and 63 homicides per year in Missouri." The study
controlled for other variables that might affect homicides, including "changes in rates of unemployment, poverty, incarceration, burglary, law enforcement officers per capita, and the presence of four other types of state laws."
Scholarly surveys In a survey published by the
New York Times in January 2017, a panel of 32 scholars of criminology, public health, and law rated universal background checks as the most effective policy to prevent gun deaths, ranking it #1 of 29 possible gun-related policies (7.3 on a 10-point effectiveness scale). In a subsequent expert survey published in October 2017 on policies to curb mass shooting deaths specifically, the expert panel ranked universal checks for gun buyers and universal checks for ammunition buyers as 6.6 and 6.5 (on a 10-point effectiveness scale), respectively, ranking them as the fifth- and sixth-most effective of 20 gun-policy proposals. A survey by Arthur Berg,
Gary Mauser, and
John Lott, published in the winter 2019–2020 edition of the
Cato Institute quarterly
Regulation, asked respondents (38 criminologists, 32 economists, and 50 public health researchers who had published an empirical study on firearms in a peer-reviewed journal) to rank the effects of 33 firearms policies (20 policies in the
New York Times in 2017, plus 8 additional policies that would loosen gun regulation, and 5 additional restrictive policies) on reducing murder rates and mass shootings. (Berg, Mauser, and Lott asked about "murder rates" rather than gun homicides because they made the assumption that stricter gun laws would not affect the homicide rate.) Respondents ranked universal background checks 13th and 14th for reducing the murder rate and reducing mass shootings, respectively. Public health researchers were substantially likelier than economists and criminologists to rate universal background checks as effective. ==Implications for mental health counseling==