Mass violence

Recent mass shootings in Buffalo, New York, and Uvalde, Texas, have — like other mass shootings before them — prompted urgent calls for policy reform. Such shootings are unusually common in the United States. Many point to easy access to guns as the primary driver of such attacks; others point to limited security or insufficient access to mental health care. The most effective way to reduce the frequency or severity of such attacks may depend on how one defines the incidents of interest. Here we are focused on violent attacks in public places that target multiple people. We exclude more common violent incidents such as gang-related violence or violence conducted with a specific profit motive. We use the phrase “mass violence” to include attacks with other weapons (such as bombs or vehicles), but currently in the United States the vast majority of such attacks are shootings.

In this survey, we asked the Criminal Justice Expert Panel to consider three statements about mass violence. Their responses are below. (Survey conducted in June 2022.)

Responses

Red flag laws, allowing police or family members to petition a court to temporarily remove firearms from a person who presents a danger to themselves or others, would reduce the frequency or severity of mass violence. - participant responses

Participant	Vote	Confidence	Comment
Paul Heaton University of Pennsylvania	Neutral/No Opinion	2
John Pepper University of Virginia	Neutral/No Opinion	3	While the logic makes sense, there is no evidence.
Aaron Chalfin University of Pennsylvania	Agree	2	In a country with several hundred million guns, red flag laws are a critical tool as they address risks posed by people who have access to existing weapons. It seems likely that some killings could have been avoided with proactive actions taken by family members/police and laws that support those actions. That said, there isn't much high quality evidence on the effects of these laws.
Santiago Tobón Universidad EAFIT	Agree	8
David Kirk University of Oxford	Agree	1	As made clear in RAND's Gun Policy in America project, research on the effects of many gun policies on various outcomes, including mass violence, is inconclusive or nonexistent because of a lack of investment in gun violence research and/or a lack of data. Many experts on the panel will surely be aware of what the Dickey Amendment did to federal funding for gun research. The relationship between red flag laws and mass violence is one question where more reseach is needed.
Giovanni Mastrobuoni Collegio Carlo Alberto	Strongly Agree	10
Patrick Sharkey Princeton University	Agree	3	Mass shootings defined in terms of high-fatality incidents where the violence is not related to other criminal activity are rare enough that we don't have any solid evidence about what makes them less common. I am thus interpreting the question as whether the policy reduces gun violence. In this case there are mixed results, but there is enough suggestive evidence to think that this approach could merit consideration.
David Weisburd George Mason University	Agree	7
J.J. Prescott University of Michigan	Strongly Agree	8
Randi Hjalmarsson University of Gothenberg	Disagree	5	I think there is increasing evidence that red flag laws reduce gun suicide rates, but not a strong evidence base that they impact mass violence. I do not think one can generalize the findings from suicide.
Rosanna Smart RAND Corporation	Neutral/No Opinion	5	While we have some evidence from California that ERPOs are often used to intervene in instances where individuals have threatened mass violence, the most common use of ERPOs are to intervene in instances of expressions or concerns of suicidal behavior. I do not believe we have strong evidence one way or another of the extent to which these laws would prevent or reduce mass violence (as defined in the preamble).
David Harding University of California - Berkeley	Agree	7
John Donohue Stanford University	Agree	9	If sensibly implemented, it should catch a least a few violence-prone individuals. Not likely to have a large effect though.
William Horrace Syracuse University	Strongly Agree	10
Alex Tabarrok George Mason University	Disagree	8	Doubtful. A lot of the time the family is also crazy and/or absent. Petitioning a court is a big deal as is removing someone's constitutional right based on someone else's say so--agree or not this is going to be a slow, convoluted process.
Stephen Billings University of Colorado - Boulder	Neutral/No Opinion	7	I agree with the policy but worry that many potential shooters would not always be know to family members/police or family members would be unlikely to petition the court even if they have concerns.
Michael Makowsky Clemson University	Agree	7
Greg Midgette University of Maryland	Agree	8	These laws require education and buy-in. If people don't know the law exists or if they don't use the law to intervene, its benefits will be limited.
Tom Clark Emory University	Agree	7
Benjamin Hansen University of Oregon	Agree	7
Morgan Williams, Jr. New York University	Neutral/No Opinion	8
Anna Bindler University of Cologne	Agree	8
Peter Reuter University of Maryland	Strongly Disagree	8
Manisha Shah University of California - Los Angeles	Agree	8
Ayobami Laniyonu University of Toronto, St. George	Neutral/No Opinion	3
David Abrams University of Pennsylvania	Neutral/No Opinion	3	My intuition is that the impact of these types of policies would be weak, given that they often require individuals close to a suspect to involve law enforcement or the courts.
Robert Apel Rutgers University	Agree	5	So little research on this because states have only begun enacting the law in sufficient numbers in the last few years. Good reason to believe it can reduce certain forms of gun deaths, namely suicides and domestic homicides—neither of which constitutes mass violence. It is also one thing to enact a red flag law and another to apply it, so any impact is likely to be small if petitions are infrequent or the pool of eligible petitioners is shallow.
Emily Owens University of California - Irvine	Agree	7
Jamein Cunningham Cornell University	Agree	6	The question then becomes, under what grounds can the court remove a firearm, and how should we interpret the Second Amendment. There will be scenarios where firearms are removed when the person poses no threat.
Monica Deza City University of New York	Strongly Agree	9	Especially for individuals with mental health issues, firearms could be confiscated during episodes of medication adjustment. Due to the cyclical nature of mental health issues, this would be particularly helpful.
Allison Harris Yale University	Neutral/No Opinion	5
Paolo Pinotti Bocconi University	Strongly Agree	7
Amanda Agan Rutgers University	Neutral/No Opinion	3	Mass violence is a rare event that is hard to measure causal impacts on. These laws would presumably reduce the number of people with guns if some are taken away and most evidence would imply fewer guns would reduce murders (see e.g. Duggan 2001 but there is debate in this literature), but I'm less certain we have causal evidence they would reduce "mass violence" and if they can be targeted correctly.
Anna Harvey New York University	Disagree	1	Courts to date have set a high bar for the "dangerousness" standard; only about 9/1000 individuals with serious mental illness are committed annually under this standard (SAHMSA 2019). Applying this standard to firearms possession is unlikely to make a large difference to mass violence, but we don't have clear evidence either way.
Kevin Schnepel Simon Fraser University	Agree	8
Jillian Carr Purdue University	Agree	5
Jennifer Doleac Texas A&M University	Neutral/No Opinion	3	I suspect this would be a worthwhile policy, because it would probably reduce suicides. It's possible it could also prevent some mass shootings, but if someone determined to cause harm in a mass violent attack can't get a gun they might use an explosive or other weapon.
Felipe Goncalves University of California, Los Angeles	Agree	2

Universal background checks, which would require almost all firearm sales in the US to go through the National Instant Criminal Background Check System, would reduce the frequency or severity of mass violence. - participant responses

Participant	Vote	Confidence	Comment
Paul Heaton University of Pennsylvania	Agree	4
John Pepper University of Virginia	Neutral/No Opinion	1	While the logic makes sense, there is very little credible evidence.
Aaron Chalfin University of Pennsylvania	Disagree	5	Most firearms used in mass killings were purchased legally so there is potentially some promise in more extensive regulation of gun sales. That said, while there are notable exceptions (e.g., private sales), most gun sales in the US are already subject to a background check. Typically the future mass shooter was legally permitted to purchase the weapon in question. Most of the evidence does not suggest that gun shows and the like lead to an immediate change in homicides.
Santiago Tobón Universidad EAFIT	Agree	8
David Kirk University of Oxford	Agree	2	Here again, we need more research, as findings to date are largely inconclusive.
Giovanni Mastrobuoni Collegio Carlo Alberto	Strongly Agree	10
Patrick Sharkey Princeton University	Agree	3	Again, my response is in relation to all gun violence. I think there is enough evidence on background checks and gun violence to "agree" with the statement.
David Weisburd George Mason University	Agree	7
J.J. Prescott University of Michigan	Agree	3
Randi Hjalmarsson University of Gothenberg	Neutral/No Opinion	5	Most research -- especially that which is causal -- does not focus on mass shootings (which still make up a small proportion of gun violence). I think there is some evidence that universal background checks may reduce mass violence, but i think more research is needed.
Rosanna Smart RAND Corporation	Neutral/No Opinion	5	The few studies that have examined the relationship of universal background checks with incidence, frequency, or severity of mass shootings have tended to find inconclusive and highly imprecise estimates of their effects. Given that many perpetrators of mass shootings (as defined in the preamble) obtain their firearms legally (i.e., are able to pass a background check), this may limit the role of this policy as a means of deterring mass violence; overall, the evidence is unclear to this point.
David Harding University of California - Berkeley	Neutral/No Opinion	8
John Donohue Stanford University	Agree	5	Yes, if we raise the age to buy guns and improve the information in the background check system and punish straw purchasers, this should stop some cases.
William Horrace Syracuse University	Strongly Agree	10
Alex Tabarrok George Mason University	Agree	6	There were 39.3 million federal and state background checks in 2020, accounting for a majority of gun purchases. A few more may help but probably not that much.
Stephen Billings University of Colorado - Boulder	Agree	8	I believe additional limits and even bans on semi and automatic weapons would be one of the most effective policies in reducing mass shooting events without being overly restrictive on basic gun rights.
Michael Makowsky Clemson University	Agree	7
Greg Midgette University of Maryland	Agree	8	Illicit market sales and transfers will still exist, so some (hopefully small) portion of attacks would still occur. That doesn't mean it isn't a worthwhile policy; it means the policy isn't sufficient by itself.
Tom Clark Emory University	Agree	7
Benjamin Hansen University of Oregon	Agree	7
Morgan Williams, Jr. New York University	Agree	8
Anna Bindler University of Cologne	Neutral/No Opinion	6
Peter Reuter University of Maryland	Agree	9
Manisha Shah University of California - Los Angeles	Agree	8
Ayobami Laniyonu University of Toronto, St. George	Neutral/No Opinion	3
David Abrams University of Pennsylvania	Neutral/No Opinion	4	Again, I would expect the impact to be relatively weak, since many perpetrators have no prior record.
Robert Apel Rutgers University	Strongly Agree	8	Some recent high-profile incidents involve people who would not have been flagged in criminal background checks, but they do appear have a modest impact on gun violence, although it is hard to say whether they reduce mass violence. That said, when combined with other control measures (e.g., licensing and permitting, waiting periods) and expanded to include private purchases, universal background checks would unquestionably reduce gun violence, including mass violence.
Emily Owens University of California - Irvine	Agree	4	There are many other ways to acquire a gun, and this could lead to a spike in gun sales in anticipation of such a requirement. But in the medium term this would make one pathway to gun ownership more costly for some.
Jamein Cunningham Cornell University	Neutral/No Opinion	1	I'm not sure that how guns are purchased is the issue with mass shootings. I believe it's more of a matter of what interventions can be put in place to reduce the likelihood that an individual takes violent actions against a group of people and the type of guns that are available to be used to commit such acts.
Monica Deza City University of New York	Strongly Agree	8	To the extent that there is escalation of violence, background checks could prevent domestic homicides or repeated assaults from escalating to homicide. Mass violence may not be preceded by several incidents.
Allison Harris Yale University	Neutral/No Opinion	5
Paolo Pinotti Bocconi University	Disagree	6	I'm afraid that anybody who really wants to get a gun would find a way around the background checks
Amanda Agan Rutgers University	Neutral/No Opinion	3	Mass violence is a rare event that is hard to measure causal impacts on. Background checks would presumably reduce the number of people getting guns (as some wouldn't pass) and most evidence would imply fewer guns would reduce murders (see e.g. Duggan 2001 but there is debate in this literature), but I'm less certain we have causal evidence they would reduce "mass violence". A paper by Gius (2017) implies that private sale background checks do not statistically impact school shootings.
Anna Harvey New York University	Disagree	1	From news reports, many individuals who commit mass violence do not have criminal records that would prevent them from purchasing firearms. Extending criminal records checks is unlikely to have a large impact on mass violence, but we don't have clear evidence either way.
Kevin Schnepel Simon Fraser University	Strongly Agree	9
Jillian Carr Purdue University	Agree	2	I think that the efficacy of this type of policy really depends on the strength of implementation. Which loopholes exist and the coordination of getting local and state information to the national database in a timely manner could impact how effective the system is.
Jennifer Doleac Texas A&M University	Neutral/No Opinion	3	Again, it's possible making it more difficult to purchase firearms could prevent some mass shootings, but if someone determined to cause harm in a mass violent attack can't get a gun they might use an explosive or other weapon. There is no empirical evidence either way.
Felipe Goncalves University of California, Los Angeles	Neutral/No Opinion	2

Increasing the presence of armed security at schools and other public venues would reduce the frequency or severity of mass violence. - participant responses

Participant	Vote	Confidence	Comment
Paul Heaton University of Pennsylvania	Neutral/No Opinion	1
John Pepper University of Virginia	Neutral/No Opinion	3
Aaron Chalfin University of Pennsylvania	Neutral/No Opinion	1	If you have a SWAT team at every significant public venue in the US, this seems likely to reduce the number of killings. But the costs of doing so would likely be prohibitive. My sense is having a police officer at every school might reduce the deadliness of mass shootings if the officer is able to engage the shooter more quickly. But this is an open question and there's not a lot of strong evidence since mass shootings, while concerning, remain rare.
Santiago Tobón Universidad EAFIT	Neutral/No Opinion	8
David Kirk University of Oxford	Disagree	3	Again, we need more investment in research and evidence. Beyond the question of whether armed security in schools might prevent or reduce the severity of mass violence, policy-makers need to consider the potential damage to educational engagement and attainment from treating schools like prisons.
Giovanni Mastrobuoni Collegio Carlo Alberto	Disagree	5
Patrick Sharkey Princeton University	Neutral/No Opinion	1	I have not seen strong enough evidence on this question to make a strong conclusion. Armed security probably reduces violence in public spaces generally, but the literature on schools that I've read is not clear. Equally or more important than the effects on violence are the potential costs and harm from turning to armed security in schools--we should be looking at other outcomes, like school discipline, academic performance, sense of belonging alongside outcomes related to violence.
David Weisburd George Mason University	Strongly Agree	9
J.J. Prescott University of Michigan	Neutral/No Opinion	5
Randi Hjalmarsson University of Gothenberg	Disagree	5
Rosanna Smart RAND Corporation	Neutral/No Opinion	5	I am not aware of any empirical, causal evidence on the extent to which the presence of armed security at schools and other public venues affects the likelihood or severity of mass violence. While a recent study (Peterson, Densley, & Erickson, 2021) found a positive association between armed officer presence and increased casualties in school shootings, its cross-sectional nature and other limitations preclude a causal interpretation.
David Harding University of California - Berkeley	Disagree	8
John Donohue Stanford University	Disagree	4	Like the oher measures, this has the possibility to at least stop some violent acts but it has 2 drawbacks compared to the earlier two: 1) it is very costly with 100,000 schools in the US, and 2) it might just shift the violence to a less hardened target
William Horrace Syracuse University	Agree	7
Alex Tabarrok George Mason University	Neutral/No Opinion	5	Displacement seems likely. Also sends the message that you need to have a gun to protect yourself which could mean more guns overall.
Stephen Billings University of Colorado - Boulder	Disagree	8
Michael Makowsky Clemson University	Disagree	6
Greg Midgette University of Maryland	Neutral/No Opinion	7	School resource officers might deter mass shootings (we don't have a strong counterfactual against which to judge), but they clearly aren't sufficient to make the threat of school violence in U.S. comparable to other wealthy nations. These police positions are typically staffed for rule enforcement, not as a rapid-response force against catastrophic violence. I worry that parents and stu might face big intangible costs in terms of intellectual and social development if schools become fortresses.
Tom Clark Emory University	Disagree	6
Benjamin Hansen University of Oregon	Neutral/No Opinion	5	Those committing mass violence often seek environments with little protection or security. So this may hold true to some degree, but I'm not sure if it would just displace the violence elsewhere. There's also other consequences to armed police forces or security in public schools.
Morgan Williams, Jr. New York University	Neutral/No Opinion	7
Anna Bindler University of Cologne	Disagree	7
Peter Reuter University of Maryland	Strongly Disagree	10
Manisha Shah University of California - Los Angeles	Neutral/No Opinion	6
Ayobami Laniyonu University of Toronto, St. George	Neutral/No Opinion	3
David Abrams University of Pennsylvania	Neutral/No Opinion	4	There is good evidence about police deterring crimes, but also of displacement effects. There is less evidence about the impact of armed security. I expect this would also have some, but relatively weak effects.
Robert Apel Rutgers University	Disagree	5	“Good guy with a gun” responses to mass violence via armed security are happening in the absence of evidence. When used in schools, there are even compelling reasons to believe there are adverse tradeoffs and opportunity costs, especially with SROs. The truth is one can find an abundance of “best practices” (read, other places do this so you should too) but not evidence-based practices.
Emily Owens University of California - Irvine	Neutral/No Opinion	10	Maybe for these rare events. Researchers would need to know which schools/venues had armed security and have a credible identification strategy to answer this question.
Jamein Cunningham Cornell University	Neutral/No Opinion	1
Monica Deza City University of New York	Agree	7	To some extent an armed guard would stop a mass shooter, but that would only occur conditional on the mass shooting already having initiated. Also, given how tumultuous mass shootings would be, the most efficient way to prevent them may not be after they have initiated.
Allison Harris Yale University	Strongly Disagree	10
Paolo Pinotti Bocconi University	Strongly Disagree	7
Amanda Agan Rutgers University	Neutral/No Opinion	3	Mass violence is a rare event that is hard to measure causal impacts on. Owens (2016) showed that School Resource Officers causally reduced administrator reports of violent crimes, but this is not "mass violence" (and they also cause increases in arrests of students and have other potential negative consequences as well). The anecdotal evidence implies that armed guards did not stop recent mass violence events at schools.
Anna Harvey New York University	Strongly Disagree	3	Heavily guarded schools would likely displace mass violence to other public locations. It would be impossible to sufficiently guard every public location so as to meaningfully reduce the frequency or severity of mass violence.
Kevin Schnepel Simon Fraser University	Neutral/No Opinion	3	I am not aware of any solid evidence of a deterrence effect from armed security guards / police officers at schools.
Jillian Carr Purdue University	Disagree	4	This is a particularly challenging policy choice. Anecdotally, this security has had minimal impact on diffusing events of mass violence, and the presence of armed security, especially in schools, potentially has high costs.
Jennifer Doleac Texas A&M University	Neutral/No Opinion	3	Increasing armed security enough to thwart heavily-armed attackers, at all possible targets of attack, would be extraordinarily expensive and would make us all feel like we're living in a war zone. Even if it were effective I suspect few Americans would be comfortable with such a shift.
Felipe Goncalves University of California, Los Angeles	Disagree	3