Mark Gius, professor of economics at Quinnipiac University, studied the law's impact on public mass shootings. Gius defined this subset of mass shootings as those occurring in a relatively public place, targeted random victims, were not otherwise related to a crime (a robbery or act of terrorism), and that involved four or more victim fatalities. Gius found that while assault weapons were not the primary weapon used in this subset of mass shootings, fatalities and injuries were statistically lower during the period the federal ban [assault weapons ban] was active. (The 2018 Rand analysis noted that the federal law portion of this analysis lacked a comparison group.)
21 September 2015. Lemieux, Frederic; Bricknell, Samantha; Prenzler, Tim (2015). “Journal of Criminological Research, Policy and Practice.” 1 (3): 131–142.
A 2015 study found a small decrease in the rate of mass shootings followed by increases beginning after the ban was lifted. Using similar models, however, Gius (2018) found that assault weapon bans resulted in significantly fewer casualties (deaths and nonfatal injuries) from school shootings.
https://www.sciencedirect.com/science/article/pii/S0047272719301446 , Journal of Public Economics Volume 181, January 2020 by Michael Luca, Deepak Malhotra, Christopher Poliquin
· Luca, Malhotra, and Poliquin found uncertain effects of state assault weapon bans on the annual incidence of mass shootings.
· We find no significant effect of mass shootings on laws enacted… nor do we find a significant effect of mass shootings on the enactment of laws that tighten gun restrictions
· Overall, there are more than 30,000 gun related fatalities in the United States per year. Approximately 56% of these are suicides and 40% are homicides. The remaining 4% are accidents or incidents of undetermined intent. Mass shootings accounted for about 0.13% of all gun deaths and 0.34% of gun murders between 1989 and 2014.
· [The following information reveals part of the criteria used in this 2016 study. Other studies undoubtedly have their own criteria. Does this lack of consistency affect the conclusions of the different studies?]
· For the purpose of this paper, we define a “mass shooting” as an incident in which 4 or more people, other than the perpetrator(s), are unlawfully killed with a firearm in a single, continuous incident that is not related to gangs, drugs, or other criminal activity.
· We further restrict our analysis to cases where at least three of the fatalities were individuals unrelated to, and not romantically involved with, the shooter(s). We include spree murders—homicides that occur at multiple locations, but with no significant pause between incidents—if they result in four or more deaths.
· We assembled a list of mass shootings since 1989 from a variety of government and media sources because there is no single, comprehensive government database of mass murders.
· Participation in the FBI supplementary homicide reports SHR program is voluntary and many law enforcement agencies do not report detailed data to the FBI. We therefore supplement the FBI data with mass shootings gathered from media accounts or compiled by other researchers and journalists interested in the topic.
· We categorize shootings by whether they are public events or primarily related to domestic conflicts, and we focus on incidents in which at least three people not related or romantically involved with the shooter died.
“Effects of Assault Weapon and High-Capacity Magazine Bans on Mass Shootings,” Updated April 22, 2020, by Blau, Gorry, and Wade
…the ban significantly reduced the annual incidence of mass shootings.
According to research done by the Violence Policy Center, in 2016 one in four law enforcement officers killed in the line of duty were killed by an assault weapon.
Lee, LK; Fleegler, EW; Farrell, C; Avakame, E; Srinivasan, S; Hemenway, D; Monuteaux, MC (January 1, 2017). "Firearm Laws and Firearm Homicides: A Systematic Review," JAMA Internal Medicine. 177 (1): 106–119. :10.1001/jamainternmed.2016.7051
A 2017 review found that limited data from 4 other studies on the effects of the federal assault weapons ban do not provide evidence that the ban was associated with a significant decrease in firearm homicides.
"Assault Weapons and Large Capacity Magazines". The Educational Fund to Stop Gun Violence
A 2018 study examined the types of crime guns recovered by law enforcement in ten different cities and found that assault weapons and semiautomatic guns outfitted with large capacity magazines generally accounted for between 22% to 36% of crime guns recovered by police.
https://www.politifact.com/factchecks/2019/aug/07/bill-clinton/did-mass-shooting-deaths-fall-under-1994-assault-w/ “Did mass shooting deaths fall under the 1994 assault weapon ban?” by Jon Greenberg, August 7, 2019
· The topic is riddled with tough data challenges. The law banned only certain types of semi-automatic firearms along with magazines holding more than 10 rounds of ammunition. Should rampages using other kinds of assault-style weapons count? Plus, mass shootings happen much less frequently than other gun crimes, which puts any scientific analysis at a disadvantage.
· The evidence shows that mass shooting deaths rose in the years after the ban. The drop during the ban is less clear cut.
· In a key 2004 study commissioned by the U.S. Justice Department, researcher Christopher Koper wrote, "The ban’s exemption of millions of pre-ban assault weapons and large capacity magazines ensured that the effects of the law would occur only gradually."
· "Should it be renewed, the ban’s effects on gun violence are likely to be small at best and perhaps too small for reliable measurement," Koper wrote.
· According to a 2019 study from New York University’s School of Medicine led by epidemiologist Charles DiMaggio, found that in raw numbers mass shooting deaths fell during the years of the ban, and rose afterwards. The death toll from mass shootings went from 4.8 per year during the ban years to 23.8 per year afterwards.
· There’s room for debate over what happened to death rates, in contrast to raw numbers, before and during the ban.
· "There is some evidence they actually declined — or at least didn’t continue to increase during the period of the ban," DiMaggio said.
· On the key policy question of whether the ban drove the decline, DiMaggio urges caution. "It is pretty much impossible to prove cause and effect," he said.
· Economist Rosanna Smart at RAND, a consulting nonprofit research group, agreed that mass shootings rose after the ban ended, but noted, "I don’t think (DiMaggio’s) methods are well-suited for determining the causal impact of the assault weapons ban."
· In a 2018 article, Smart reviewed two studies on the impact of the ban. She said strictly in terms of statistical methods, the results were "inconclusive." Although one report did find that state-level bans were effective at reducing mass shooting death rates.