Posted BY: National Institute Of Justice-Rand


The latest data on mass shootings from the National Institute of Justice of the US Department of Justice and the Rand Corporation.

There are no standard definitions of mass shootings. There are no easy answers.

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I was interviewed on a national television show about research-based answers to mass shootings. Beyond condemning those involved, I stumbled. I knew that there were few (if any) firm answers or guidance.

That’s not the case for some doing similar interviews. Many are quick to promote firearm controls or red flag laws or suggest that there are effective answers. That’s simply not the case. The complexities and price tags for the proposals are immense.

For example, we within the justice system acknowledge our inability to keep track of convicted-fingerprinted felons and maintain accurate records. There are vast inaccuracies. Now, we want to do national or state databases for those with ever-changing mental health conditions?

It will be a logistical and financial nightmare with probable ACLU challenges. It’s not going to work beyond those committed to institutions and even then, conditions change.

As of this writing, the latest Congressional proposals are available via CNN.

It’s time to examine the best available data on the subject. Note that varied definitions of mass shootings and whether they were public (inferring unknown victims) or private (inferring known victims) will be difficult to follow. Previous research suggests that most victims of mass shootings were known to the shooter.

There are few firm conclusions based on research. Policy issues are elusive. The emphasis is on assault weapons when the overwhelming majority of mass shootings involve handguns (while noting that many mass shooters carry a variety of weapons).

You’re going to get different policy perspectives from different groups, see Politico.

Policy Solutions to Address Mass Shootings was offered by the National Institute of Justice and Rockefeller Institute of Government in August of 2021.

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The Best Available Data

What “is” useful is a 2021 document from the National Institute of Justice of the US Department of Justice and the Rand Corporation (one of the best crime-related research organizations in the nation) summarizing what we know and don’t know about mass shootings. What’s below is from that document. It’s a tool kit for understanding “and” responding to mass shootings.

Most will be a bit frustrated by the lack of clarity as to what constitutes a mass shooting, who commits them, their mental health issues, and what can be done.

Those in law enforcement are exasperated by the national call for cops to be guardians, not warriors which seem wildly misplaced because law enforcement is expected to enter a mass shooting and stop the shooter, which requires endless tactical training and equipment.

In an earlier article, I point out that the great majority of what we call gun violence is street-level violent crime, not mass shooters. I suggest that the explosion of media coverage of mass shootings is somewhat misplaced; the vast majority of victims of gun violence are people of color and society has become immune to that violence.

It’s also important to point out that the overwhelming majority of mass shootings (77 percent) involve handguns, not assault weapons per another research project from the National Institute of Justice. You are going to discover some differences in this document (and others) versus the current Rand Corporation research. For example, 40 percent (below) broadcasted their shooting intentions versus 48 percent in previous research.

Yet what’s below is useful-necessary as to understanding the issues and being ready for a response.

Passages below are selected, rearranged, and edited for brevity from Rand. Most are direct quotes.

Who Commits Mass Shootings?

According to this literature, the perpetrators of mass public shootings in the United States have been overwhelmingly male (98 percent) and are most commonly non-Hispanic White (61 percent). In addition, they are most commonly younger than age 45 (82 percent); more specifically, 26 percent of mass public shooters from 1976 to 2018 were younger than age 25, 27 percent were aged 25 to 34, and 29 percent were aged 35 to 44.

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Relative to the overall U.S. population, mass public shooting offenders are much more likely to be male and are somewhat younger; relative to other homicide offenders, males and non-Hispanic Whites are overrepresented among mass public shooters, and mass public shooters are older.

For comparison, of the overall U.S. population in 2019, approximately 49 percent was male, 60 percent was younger than age 45, and 60 percent was non-Hispanic White (U.S. Census Bureau, 2020).

Of murderers in 2018 with known offender characteristics, 88 percent were men, 84 percent were younger than age 45 (38 percent younger than 25, 31 percent aged 25 to 34, and 16 percent aged 35 to 44), and 42 percent were White (Hispanic ethnicity information was not provided), (FBI, 2019).

Even if we did have definitive and complete data sources on the characteristics of all mass shooting incidents, it is still likely to be exceedingly difficult to identify useful predictors of mass shootings. With the exception of male sex, risk factors that appear to be overrepresented among mass shooters relative to the general population are often still uncommon among offenders on an absolute level.

Thus, even if one could find a way to prevent individuals with a documented serious mental illness from committing a mass shooting—for example, developing and delivering effective treatments to more than 10 million Americans or effectively preventing their access to firearms—most mass shootings would still occur because only a fraction of mass shootings are committed by individuals with a documented history of serious mental illness.

Mental Health And Mass Shootings

Media coverage often links mass public shootings with serious mental illness, but estimates of the prevalence of mental illness among mass public shooting offenders vary widely depending on the types of incidents considered and the methods used to define and identify mental illness.

Rates of formal diagnoses of psychotic disorders (including diagnoses made post-incident, which may be affected by the incident itself) among mass public shooters are estimated to be about 15 to 17 percent.

Studies that use a broader definition of mental illness and consider informal evidence indicative of mental health problems (e.g., statements by law enforcement or family before or after the incident) have found prevalence rates ranging from 30 to 60 percent. This informal evidence, which is often obtained subsequent to the incident, is invariably affected by the act of mass violence itself.

It does not suggest that mental illness is useful for predicting a subsequent mass shooting.

Of note, a study of 106 perpetrators of mass public shootings in the United States between 1990 and 2014 found that less than 5 percent of offenders had a history of involuntary commitment or adjudication of dangerousness that would have prohibited them from purchasing a firearm following the federal mental health background check.

Although most research supports that, overall, people with serious mental illness are overrepresented among mass public shooters, this does not imply that serious mental illness causes mass shootings, just as we cannot conclude that being a young man causes mass shootings.

Domestic Violence-Criminal Histories And Mass Shootings

Other researchers and analysts have noted that many mass shooters have a history of domestic violence. Using three mass shooting databases (whose underlying data sources include media reports, court records, and police records) and their own search of criminal records, Zeoli and Paruk (2020) analyzed 89 individuals who perpetrated a mass shooting (involving four or more fatalities, excluding the offender) between 2014 and 2017.

Of the 89 individuals, 28 (31 percent) had a history of suspected domestic violence. The authors identified that, of those 28, seventeen (61 percent) had prior interaction with the criminal justice system related to domestic violence, and six individuals had a felony or misdemeanor conviction for domestic violence.

Using a different definition of mass shooting (involving four or more casualties, including the perpetrator, and excluding felony-related mass shootings), Gu (2020) found that 36 percent of mass shooting incidents from 2014 to 2019 involved an offender with a history of domestic violence or violence against women.

“Public” Mass Shootings Are Responsible For Less Than 0.5 Percent Of All Homicides

Incidents of mass firearm violence galvanize public attention. There has been extensive media coverage of many incidents in the United States in which individuals have used firearms to kill large numbers of people. These mass public (emphasis added) shootings are rare events—they constitute less than 15 percent of all mass killings in the United States and are responsible for less than 0.5 percent of all homicides but they have far-reaching impacts on citizens’ mental health, anxiety, and perceptions of safety.

Editor’s note, see below for a discussion of “public” mass shootings.

No Firm Definitions of Mass Shootings

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There is no standard definition of what constitutes a mass shooting, and different data sources—such as media outlets, academic researchers, and law enforcement agencies—frequently use different definitions when discussing and analyzing mass shootings.

For instance, when various organizations measure and report on mass shootings, the criteria they use in counting such events might differ by the minimum threshold for the number of victims, whether the victim count includes those who were not fatally injured, where the shooting occurred, whether the shooting occurred in connection to another crime, and the relationship between the shooter and the victims.

These inconsistencies lead to different assessments of how frequently mass shootings occur and whether they are more common now than they were a decade or two ago.

Because mass shootings that stem from domestic and gang violence are contextually distinct from high-fatality indiscriminate killings in public venues, some analysts have argued that they should be treated separately.

In their analyses of “mass public shootings,” Lott and Landes (2000) excluded any felony-related shooting, and Duwe, Kovandzic, and Moody (2002) excluded incidents where “both the victims and offender(s) were involved in unlawful activities, such as organized crime, gang activity, and drug deals.”

Similarly, other researchers have restricted analyses to events that occurred in a relatively public area and in which victims appeared to have been selected randomly.

However, others have claimed that this narrow definition ignores a substantial proportion of gun-related violence from family-or felony-related murder. Furthermore, determinants of whether victims were selected indiscriminately or whether the incidents were gang- or crime-related are, to some degree, subjective. Accurate information about the shooter’s motivations or connection to gangs may not have been included in police or news reports of the incidents.

How Many Mass Shootings Occur In A Year?

The number ranges from 10 to 503 in 2019 given group or research decisions as to what constitutes a mass shooting, the location (public or private), and the number of victims.

Have Mass Shootings Increased?

The data from multiple studies suggest a slight increase in the incidence rate of mass public shootings over the past four decades. From 2016 to 2018, the annual rate of mass public shooting incidents was about one incident per 50 million people in the United States.

Considering the number of fatalities in these shootings, this corresponds to approximately 0.4 percent of all homicides, or approximately 0.2 percent of all firearm deaths, over that period.

However, using an expanded definition of mass shootings that includes domestic-or felony-related killings, there is little evidence to suggest that mass shooting incidents or fatalities have increased.

Adjusted for changes in the size of the U.S. population, the incidence of all mass shootings (four or more fatally injured victims, excluding the offender, regardless of shooter motivation or circumstances) was highest in the late 1980s and early 1990s, averaging one incident per 10 million people from 1989 to 1993. More recently, between 2016 and 2018, the annual rate of all mass shooting incidents was about one incident per 14 million people.

Considering the number of fatalities in these mass shootings, this corresponds to approximately 0.8 percent of all homicides, or approximately 0.4 percent of all firearm deaths, over that period.

Thus, different choices about how to define a mass shooting result in different findings for both the prevalence of these events at a given time and their frequency has changed over time.

Locations And Motivations Change Over Time

Even the subset of mass public shootings seems to encompass a variety of offender types, and some researchers have suggested that the relative prevalence of these offender typologies has changed over time. When Capellan and colleagues considered incidents in which an offender used a firearm to kill or “attempt to kill” four or more victims in a public setting, they found that school shootings constituted the majority of mass public shooting incidents in the 1960s and 1970s, and workplace shootings became increasingly prevalent in the 1980s to 2000s.

The past decade has seen an increase in the percentage of mass public shootings that are posited to relate to fame-seeking on behalf of the individual or on behalf of a broader ideology.

Some researchers have suggested that this rise in fame‐ and attention‐seeking motivations among mass public shooters has contributed to an escalation in the lethality of these incidents.

Planning Mass Shootings-Public Statements

Although there are some noted differences across different types of mass public shootings, an overarching commonality is that most incidents are preceded by some level of planning by the shooter. Among active shooting cases from 2000 to 2013 for which sufficient information was available, 62 percent of offenders planned the attack for more than one month, and 9 percent planned for more than one year.

Focusing on incidents involving eight or more fatally injured victims, Lankford and Silver (2020) found that at least half of the 18 high-fatality mass public shootings between 2010 and 2019 involved a planning period of one year or longer.

About 40 percent of mass public shooters make some form of verbal or written threat (e.g., threats made in front of family or friends or posted to social media) prior to the incident.

Firearms Used

It is common for multiple firearms to be involved in public shootings: Various studies have indicated that multiple firearms were involved in an estimated 34 percent of active shooting incidents across 2000–2017, 42 percent of mass public shooting incidents across 1999–2013, and 79 percent of mass public shooting incidents that resulted in eight or more fatalities across 1966–2019.

In an analysis of mass public shootings in which shooters attempted to kill at least four individuals, Capellan and Jiao (2019) found that 80 percent of offenders had prior access to a firearm, although 41 percent of those individuals obtained additional firearms for the incident.

Handguns are the firearm most commonly involved in active shootings and mass shootings; semiautomatic rifles or “assault-style” weapons are used in an estimated 10 to 36 percent of active shootings and mass shootings.

The use of large-capacity magazines (LCMs) is more common in mass public shootings and high-fatality mass shooting incidents than it is in firearm crimes overall. The estimated prevalence of LCM involvement in mass shootings ranges from 20 to 60 percent, or from 45 to 60 percent when restricting the denominator to mass public shootings or high-fatality mass shootings.

For comparison, LCM-equipped firearms are estimated to constitute 22 to 36 percent of crime guns recovered by police in most urban jurisdictions.

Assault Weapons

When counting incidents involving an assault weapon or semiautomatic rifle per year, it ranges from 10 to 44.

Research On Policies That Might Reduce Mass Shootings

Because individuals who perpetrate mass shootings often die by suicide (or expect to be killed by someone trying to stop the shooting), standard deterrence strategies used in crime prevention are unlikely to work; increasing the certainty or severity of punishments seems unlikely to be effective when the perpetrator already expects to die in the mass shooting.

However, mass shootings are sufficiently rare that the statistical assumptions of these methods rarely hold, threatening the validity of the effect estimates and statistical inference and potentially resulting in spurious effects.

Even in studies that use models more appropriate for the distributional characteristics of mass shooting outcomes, the high degree of variability in mass shooting prevalence, injuries, and fatalities makes analyses of the effects of state policies on mass shooting outcomes subject to extremely low statistical power.

Using data from 1989 to 2014, researchers found a 15-percent increase in the number of state firearm bills introduced in the year following a mass shooting; states with Democratic-controlled legislatures did not show significant effects of firearm laws enacted, while states with Republican-controlled legislatures were significantly more likely to enact more-permissive gun laws subsequent to a mass public shooting incident in the state.

If mass public shootings are a cause rather than (or in addition to) a consequence of firearm policy, models that fail to appropriately account for this reciprocal relationship may produce biased and misleading estimates of the effects of laws on mass shootings.

Finally, although extreme risk protection orders are most commonly requested because of concerns about self-harm, a detailed review of case records from 159 such orders issued in California found that 21 (13.2 percent) involved an individual who had access to or was planning to access firearms and expressed or exhibited behavior suggesting intent to perpetrate a mass shooting.

These analyses do not directly assess the causal effect of policies on mass shooting outcomes, but they can still provide important insights for crafting and implementing policies.

(Editor’s note, the following sentence is from another part of the document). Implementing broader violence prevention strategies rather than focusing specifically on the most extreme forms of such violence may be effective at reducing the occurrence and lethality of mass shootings.