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

• Author: Daniel W. Webster,Elizabeth A. Stuart,Marisa D. Booty,Alexander D. McCourt,Cassandra K. Crifasi
• Date: 01 February 2020
• DOI: http://doi.org/10.1111/1745-9133.12487
• Published date: 01 February 2020

DOI: 10.1111/1745-9133.12487

SPECIAL ISSUE ARTICLE

COUNTERING MASS VIOLENCE IN THE UNITED STATES

Evidence concerning the regulation of firearms

design, sale, and carrying on fatal mass shootings

in the United States

Daniel W. Webster Alexander D. McCourt Cassandra K. Crifasi

Marisa D. Booty Elizabeth A. Stuart

Johns Hopkins University

Correspondence

DanielW. Webster,Johns Hopkins University

BloombergSchool of Public Health, Center for

GunPolicy and Research, 624 N. Broadway,

Room580, Baltimore, MD 21205-2103.

Email:dwebster@jhu.edu.

Fundinginformation

TheJoyce Foundation; Bloomberg American

Health Initiative

Research Summary: We used data from the FBI’s

Supplemental Homicide Reports and other publicly avail-

able databases to calculate state-level annual incidence

of fatal mass shootings for 1984–2017. Negative bino-

mial regression models were used to estimate the asso-

ciations between changes in key gun laws and fatal

mass shootings. Handgun purchaser licensing laws and

bans of large-capacity magazines (LCMs) were associated

with significant reductions in the incidence of fatal mass

shootings. Other laws commonly advocated as solutions

to mass shootings—comprehensive background checks,

assault weapons bans, and de-regulation of civilian con-

cealed carry of firearms—were unrelated to fatal mass

shootings.

Policy Implications: Our findings suggest that lawsrequir-

ing firearm purchasers to be licensed through a background

check process supported by fingerprints and laws banning

LCMs are the most effective gun policies for reducing fatal

mass shootings.

KEYWORDS

mass shooting, gun regulation, EVALUATION

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in

any medium, provided the original work is properlycited.

© 2020 The Authors. Criminology & Public Policy published by WileyPeriodicals, Inc. on behalf of Amer ican Society of Criminology

Criminology & Public Policy. 2020;19:171–212. wileyonlinelibrary.com/journal/capp 171

172 WEBSTER ET AL.

High-profile public mass shootings (e.g., incidents that gain significant media attention as a result of

high victim count and/or unique characteristic such as location or motive) prompt what have become

predictable responses across the political spectrum. One side points to easy firearm access as the

key cause of mass shootings and calls for stronger gun laws including comprehensive background

checks, bans on assault weapons and large-capacity magazines (if those wereused), and more recently,

Extreme Risk Protection Order (ERPO) laws to disarm persons planning violent acts. The other side

sees unarmed victims being shot in mass shootings and focuses on the hypothetical question, “What

if one of the victims or a bystander used a firearm to stop the attack?” The solutions to mass shoot-

ings that stem from this perspective include eliminating so-called “gun free zones” and reducing or

eliminating restrictions on civilian carrying of concealed firearms in public places.

In a study of fatal mass shootings in the United States during 2014–2017 with several online data

sources, Zeoli and Paruk (2020, issue) determined that 46% of the shootings were committed by some-

one who was prohibited or likely prohibitedfrom possessing a firear m. But the breadth of disqualifying

conditions for firearm possession—e.g., whether convictions for violent misdemeanors, domestic vio-

lence restraining orders (DVROs)involving dating partners, and younger than 21 years of age disqualify

someone from purchasing or possessing a firearm—vary significantly across states and determine the

size of the pool of persons at increased risk for perpetrating firearm violence who are legally prohibited

from purchasing or possessing firearms (Vittes, Vernick,& Webster, 2012). Indeed, the breadth of dis-

qualifying conditions for persons with a history of violence was consistentlyassociated wit h reductions

in rates of intimate partner homicides (Zeoli et al., 2018). Because many mass shootings are committed

in the context of domestic violence or involve perpetrators with a history of domestic violence (Zeoli

& Paruk, 2020), broader firearm restrictions for DVROs and violent misdemeanors could potentially

reduce mass shootings.

Broad firearm prohibitions for violent or other criminal actions may not keep those individuals

from accessing firearms without strong background check systems.State laws requiring comprehensive

background checks(CBCs) and purchaser licensing could also potentially influence firearm availability

to individuals at risk of perpetrating a mass shooting by making it harder for prohibited persons to

obtain firearms. The typical CBC law requires prospective purchasers in private transfersof firearms to

pass a background checkt hat is facilitatedthrough a licensed firear m dealer.In contrast, most purchaser

licensing laws require prospective purchasers to apply directly at public safety agencies where they

are fingerprinted for thorough background checks that include more complete records of prohibiting

incidents and greater time available to conduct those checks than is the case for background checks

absent licensing. 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 lawsreduce homicides (Castillo-Car niglia etal., 2018; Kagawa et al., 2018;

Zeoli et al., 2018); however, there has been consistent evidence that licensing laws reduce homicides

(Crifasi et al., 2018; Hasegawa, Webster, & Small, 2019; Rudolph, Stuart, Vernick, & Webster, 2015)

and suicides (Crifasi, Meyers, Vernick, & Webster, 2015). Licensing laws could potentially suppress

fatal mass shootings, but there are no rigorous studies examining this question.

The research literature on the effects of firearm policies on mass shootings is sparse and has impor-

tant limitations. A recent study found that that higher rates of gun ownership and greater permissive-

ness of gun laws were associated with higher rates of fatal mass shootings for incidents connected to

domestic violence and other types of mass shootings (Reeping et al., 2019). Unfortunately, the gun law

permissiveness scale used in the study has not been fully described, evaluated, or validated, and it does

not allow for estimates of the effectsof specific firearm laws on mass shootings.1Furthermore, the dat a

to identify fatal mass shootings in this study—the FBI’s Supplemental Homicide Reports (SHR)—did

WEBSTER ET AL.173

not include major fatal mass shootings, including shootings at Sandy Hook Elementary School in New-

town, Connecticut, in 2012 (26 deaths); a movie theatre in Aurora, Colorado, in 2012 (12 deaths and

58 individuals with nonfatal gunshot wounds); or a church in Southerland Springs, Texas (26 deaths

and 20 nonfatally wounded). The data for this study also counted the Virginia Tech mass shooting

(32 deaths and 23 victims with nonfatal wounds) as three incidents as a result of the way that the SHR

limits the number of victims to 11 in any given homicide incident. Another recent state-levelstudy used

an open-source database compiled by the publication Mother Jones and found no association between

measures of gun ownership and gun law permissiveness and fatal mass shootingsin public places (Lin,

Fei, Barzman, & Hossain, 2018). The generally undescribed gun law permissiveness measure, how-

ever, seemed to be limited to concealed carry restrictions, and the Mother Jones database has been

criticized for inconsistent application of inclusion/exclusion criteria and for missing some cases (Fox

& Fridel, 2016).

Luca and colleagues estimated the effects of several state gun laws—CBC laws that extend back-

ground check requirements to private transfers, purchaser licensing laws, regulations over civilians

carrying concealed weapons, bans of assault weapons or large-capacity magazines (LCMs)—and the

probability that a four-fatality mass shooting occurred in a given state and year during 1989–2014

(Luca, Malhotra, & Poliquin, 2019). Unfortunately, the authors used linear regression models that vio-

lated model assumptions for binary outcomes and thus made the findings difficult to interpret.

Two recent studies, each using different data sources and different outcome measures for fatal mass

shootings, drew different conclusions regarding the association between the federal ban of assault

weapons and LCMs. Fox and Fridel (2016) used the SHR data to examine cases involvingfour or more

firearm homicide victims and found no association between the incidence of fatal mass shootings and

the presence of the federal ban of assault weapons and LCMs. It is curious that these researchers did not

examine whether the ban influenced the number of persons shot in mass shootings because the char-

acteristics of the banned products are relevant to how many shots can be fired in a short span of time.

Indeed, recent studies have documented that fatal mass shootings committed with assault weapons

and/or LCMs result in significantly more victims shot than is the case in such shootings which involved

no assault weapons or LCMs (Klarevas, 2016; Koper,2020, this issue; Koper, Johnson, Nichols, Ayers,

& Mullins, 2018). DiMaggio and colleagues (2019) published a study in which they reported that dur-

ing the period when the federal ban of assault weapons and LCMs was in place (1994–2004), fatal mass

shootings were 70% less likely to occur.But this study had major limitations based on the data used and

the lack of statistical controls for other lawchanges or social trends that might explain variation in mass

shootings. The study used data on fatal public mass shootings with four or more fatalities for the years

1981 through 2017 that were collected by three open-source databases—Mother Jones,Los Angeles

Times, and Stanford University. Inexplicably, the researchers only included cases in their analyses that

appeared in all three sources and thereby excluded many incidents of fatalmass shootings. This limited

their data to only 51 public mass shootings that presumably were the most widely publicized. The study

did not examine variation by state and thus did not consider state gun laws nor did it control for other

covariates other than linear trend. Gius (2015) estimated the effects of federal and state bans of assault

weapons and LCMs with annual data from the SHR for the years 1982–2011 and found evidence that

such bans were linked to lower rates of fatalities in mass shootings. Klarevas, Conner, and Hemenway

(2019) found that LCM bans were associated with significantly fewer incidents of high-fatality (six or

more victims) mass shootings and lower fatality rates forsuch shootings during t he period 1990–2017.

An important limitation of this study was that it did not consider the effects of any other type of

firearm laws.

In-depth studies of the circumstances surrounding public mass shootings in the United States during

2000–2017 have foundthat ar med civilians with concealed carry permits played a role in stopping mass