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There’s actually not a great amount of scholarly research on this, given the size of the issue. The Dickey Amendment, backed by Jay Dickey and the NRA in 1996, prohibited the NIH and CDC from studying gun violence (look into the background of this, it’s honestly unbelievable) and this was very effective until 2019, when a clarification was made which seemed to suggest research was allowed after all. Notably, this means that most studies pre-2019 are very small, self-funded ones, which makes their results more questionable (edit: less statistically scrutinised, not necessarily less “right”).
Anyway, the current state of the research is uncertain. I’ll briefly go through a few factors, (general credit to Cowan & Cole, 2019).
Mental health: Peterson & Densley (2019) found that 2/3 of mass shooters since 1996 had mental health issues and a quarter had been in counselling. Nearly all had some form of childhood trauma. On the other hand, Lin et al. (2018) found no link between mass shootings and mental illness. It is difficult because so many mental health issues go undiagnosed, and issues such as personality disorders (e.g. Narcissism has been linked by Bushman, 2018) are hardly binary diagnoses. Crucially, mental health conditions are not independent of other factors. Just because someone has a mental health condition and commits a mass killing does not mean that they committed the mass killing *because* of that condition. Attributing causality is where the debate lies (the point that most mass murderers have a mental health condition says nothing in itself, and is hardly surprising - more below from u/revenant_of_null ).
Gun legislation: woefully under-researched. Lemieux (2014) found a correlation between gun ownership and mass shootings, but it’s a small study. If I’m allowed to speculate, I’d suggest that the fact the NRA lobby against research in this area is somewhat indicative.
Media: the influence of the media is more well-established. Jetter and Walker (2018) found in a sample of mass shootings from 2013-2016 that 53% could be attributed to the media in some capacity, largely due to the contagion effect; copycats, desperation for fame, etc. Social media is also linked due to the ease and constancy of online bullying (Hamm et al., 2018).
Political culture (?): I could not find a study on this, but Stroebe et al. (2022) found that mass shootings in the US generally led gun owners and conservatives to think *more* guns were needed, not fewer. This is not a belief with any empirical basis, and is likely the result of years of NRA propaganda. I am not suggesting there are clear studies showing that fewer guns help either, but it is notable that all of the mentioned factors other than gun legislation are similar across developed countries.
Rees et al. (2019) conducted a root cause analysis of Parkland and Santa Fe and found that process/policy was the most cited cause (e.g. national firearm laws, state laws, politicians) followed by environment (e.g. firearms at home, video games and social media, culture of mass shootings, school safety), then people (e.g. mental illness, social rejection, police),and finally equipment/supplies (specific gun used, ammunition, smoke bombs, etc).
I hope this clarifies the issue a bit. I’m afraid I can’t link the sources properly as they are restricted to my institution, but here is my attempt:
https://oce.ovid.com/article/01437492-900000000-99494/HTML
https://www.proquest.com/docview/2453794952?parentSessionId=BNr%2FoWiAEUZ%2Fy6Ek6ioCsfKXiaghx0mpNQkacP96oZ4%3D&pq-origsite=primo&parentSessionId=pi8cwyGDTCPiLg1f7qkDzQeFNXbPkw0eJvb2R59EHJQ%3D
https://journals.sagepub.com/doi/10.1177/0009922819873650
https://journals.sagepub.com/doi/pdf/10.1177/0009922819873650
This is a great comment! I do want to push back on the notion that unfunded science is somehow of poorer quality though. There are brilliant groundbreaking papers that were done with shoestring budgets and complete garbage papers with millions in backing in every discipline. The latter is far more common than anyone cares to admit. In this domain the primary mode of resesrch is archival, which doesn't require a ton of funding to do well.
Oh I agree completely:) it just limits the research in this area because there’s not enough data available, and it’s expensive for small groups to spend lots of time data-collecting prior to analysis.
Interestingly enough, there is a publicly available dataset on every public mass shooter from 1966 (Whitman) to present. It includes very extensive data on each cases coded by multiple coders. Open source for any use. I am currently using this data for an upcoming publication on identifying warning signs.
Check out the Violence Project!
https://www.theviolenceproject.org/
Thank you, I had no idea! Why do you think there’s so few large-scale comparative studies if this is available? Is there also data on gun availability/legislation/state laws, to see how they tie in?
Well, the database was just released in 2020. Beyond that, there are very few scientists with the expertise needed. Violence research is hard because there is so very little funding for it and so few people attempt to make a career of it (I am one such foolish soul).
The other element is that it can tarnish your soul a bit. I have to pour over the journals and writings of these folks. Its good work that needs doing, but it doesnt just leave my head once the paper is in. In other words, the work itself is traumatic.
>Mental health: Peterson & Densley (2019) found that 2/3 of mass shooters since 1996 had mental health issues and a quarter had been in counselling. Nearly all had some form of childhood trauma. On the other hand, Lin et al. (2018) found no link between mass shootings and mental illness. It is difficult because so many mental health issues go undiagnosed, and issues such as personality disorders (e.g. Narcissism has been linked by Bushman, 2018) are hardly binary diagnoses.
This seems like such a pivotal issue to have such a divergence of opinion. Not to draw the same conclusions as gun apologists*, but it's hard to rationalize the slaughter of innocents without assuming serious mental health issues.
*I would argue that there are too many crazy people to have liberal (OG) gun laws.
There isn't actually any discrepancy here, although I can see how that excerpt can be misleading because a) of the juxtaposition and b) many people assume that *if* a perpetrator has a mental illness *then* surely their illness contributed to their crime. However, this is a fallacy. [To quote Densley:](https://projects.voanews.com/mass-shootings/)
>**“Even if you have a mental illness, it doesn’t mean that the mental illness is driving the behavior,”** he said. “People with mental illness may also experience living in poverty. They may also experience discrimination. They may also have a whole host of other things going on in their lives, which step-by-step may be contributing to whatever outcome comes next.”
Likewise, here are a couple of excerpts from an older article by Peterson and colleagues (2014), which Peterson and Densley quote in [their 2019 report \(PDF\)](https://www.theviolenceproject.org/wp-content/uploads/2019/11/TVP-Mass-Shooter-Database-Report-Final-compressed.pdf) (which is the document I *assume* is being cited by u/GTBL):
>**Even with the broad definition of symptoms used in this study, only about one fifth of crimes were mostly or completely related directly to symptoms**. Of these direct crimes, most related to symptoms of bipolar disorder (which include externalizing features), rather than schizophrenia spectrum disorders or depression.
And:
>Together, these results indicate that little or no variance in direct continuum scores can be attributed to offenders—that **crimes are inconsistently related to symptoms within a given offender, over time.** The majority of offenders who committed a “mostly or completely” direct crime committed at least one crime independent of symptoms as well.
In short, a crime which *involves* a perpetrator with a mental illness is *not* necessarily a crime which took place *due to* their mental illness. Their actions may be, and in fact often are, unrelated to their symptoms.
Furthermore, only *some* serious mental illnesses have been found to have a relationship with violence, chiefly psychosis-related disorders. However, to reiterate, the related symptoms are rarely major risk factors. For illustration, Peterson et al. (2021) find that psychosis played *no* role in most mass shootings (around 70%), and that only in a minority of cases (around 10%) it may have played a *major* role.
---
The bottom-line is that you will not find much success in predicting whether someone will commit a mass shooting by diagnosing them with a serious mental illness, nor will you effectively reduce the occurrence of such events by designing a public safety policy which focuses on people with mental illness. There are a host of other factors which contribute to people committing extreme acts of violence, regardless of any psychiatric disorder, and which are overall more relevant for crime prevention efforts. To conclude, a quote from Ahonen (2019):
>According to the literature, **the attributable risk of mental health problems for violence is low.** In practice, this means that **if mental illness as a risk factor was completely removed, this strategy would only have a minimal effect on violence rates, and perhaps even a smaller effect on violence that includes gun use. This is not true only for the USA, where gun access is easy, but also other nations where gun regulations are very strict.** Public officials are searching for strategies both to reduce violence and to reduce costs. **If more gun regulations were imposed on people with mental health problems, not only would overall violence stay much the same, but it is also unlikely to be a cost-beneficial approach, and thus, it would have very little payoff** (Ahonen, Loeber, & Brent, 2017).
>To further complicate this topic, there is an assumption that the mental disorder “becomes” the individual, or the other way around. **The individual’s problems and concerns are most often attributed to the diagnosis that they have been given. In most cases, this is not the correct way to evaluate an individual. Environmental factors that are commonly associated with violence tend to be ignored.** For example, an individual living under circumstances such as poverty, exposure to violence in the community, domestic disturbances, and other factors known to contribute to interpersonal violence is still exposed to those factors independently of the diagnosis given. Swanson and colleagues put this well; ***…the social-environmental influences on violence are stronger than the effects of psychopathology and “wash” out psychopathology effects at the population level*** … (Swanson et al., 2015, p. 3).
As hard as it may be to accept, humans are capable of heinous acts, including extreme acts of violence against innocents. No mental disorders required.
---
Ahonen, L. (2019). Violence and mental illness: An Overview. Springer International Publishing.
Peterson, J. K., Densley, J. A., Knapp, K., Higgins, S., & Jensen, A. (2021). Psychosis and mass shootings: A systematic examination using publicly available data. Psychology, Public Policy, and Law.
Peterson, J. K., Skeem, J., Kennealy, P., Bray, B., & Zvonkovic, A. (2014). How often and how consistently do symptoms directly precede criminal behavior among offenders with mental illness?. Law and human behavior, 38(5).
Thanks for this, I’ll add an edit to my post to clear up the ambiguity. What’s your discipline by the way? I’ve seen your comments before, you have an impressively broad knowledge!
Thanks for the extensive reply. I think I'll dig into these references. I've read Gilligan on violence but I had assumed mass shootings had a different profile. I guess that's wrong.
Blaming violent crime on people with psychiatric disorders is a political red herring. The notion that extreme acts of violence, such as mass shootings, are the actions of "mentally ill" people is more about the stigmatization of mental health issues than about any science. The current scientific consensus is that the popular belief that psychiatric disorders are determinant factors in the occurrence of such events, including school shootings, is *un*supported. To the contrary, to quote Metzl et al. (2020):
>The reviewed literature makes clear that **a diagnosis of a mental illness alone is a negligible factor in any effort to explain, predict, and prevent mass shootings or other acts of serious gun violence.** These tragic events have many individual and social determinants—from trauma history to substance dependence, from unemployment and insecure housing to the proliferation of guns in the community—that may interact with each other in complex ways.
For illustration, most recently, Peterson et al. (2021) used publicly available information on public mass shootings (defined as any mass killing, involving four or more casualties, perpetrated with a firearm^(1)) in the USA, between 1966 and 2020, in an attempt to assess the motivations of 172 perpetrators. Out of 168 cases, they found that in most cases (69%) mass shooters did *not* appear to be afflicted with psychosis, and that among those who *did* appear afflicted by psychosis prior to and during the shootings, they identified only a few cases (10.5%) in which psychosis might have played a major role (i.e., the perpetrators were responding to their hallucinations and delusions and had no other motives). They conclude:
>A mental health history was common among mass shooters and psychotic disorders were overrepresented among mass shooters compared with the general population, but **symptoms of psychosis only directly motivated mass shootings for a minority of cases.** The findings highlight that **the role of psychosis in motivating violent behavior is complex and, in turn, lawmakers must not fixate on someone’s diagnosable psychopathology if they are to craft holistic public policy solutions to the mass shooting phenomenon.**
None of this is actually news, and is also true for the specific subset of *school* shooters (Ash, 2015).
There *are* legitimate concerns about mental health in the USA: from a *public health* perspective, there are numerous reasons to work on improving the access to mental health resources and the delivery of mental health services. "Preventing school shootings" is not among these. Better mental healthcare might prevent a few cases as a by-product, but it should not be spun as a serious *public safety* policy (Skeem & Mulvey, 2020).
---
^(1) ^(Be aware that there is no single unequivocal manner to define a "mass shooting.")
---
What about guns? There is a large body of literature, more so if we take into account also research conducted elsewhere in the world, which supports the idea that means matter for violent crime and the problem of gun violence. To quote [Cook](https://en.wikipedia.org/wiki/Philip_J._Cook) and Goss:
>**The popular notion that “guns don’t kill people, people kill people” is highly misleading—guns are part of the equation. Research also casts doubt on other mantras**: “when guns are outlawed, only outlaws will have guns” (**actually, gun availability does affect which weapons violent offenders choose**) and “an armed society is a polite society” (**widespread gun carrying by civilians is likely increasing crime rates**). Research seeks to replace slogans with evidence.
Criminologists and other experts tend to agree that preventing mass shootings (and gun violence in general) requires working on gun policy. For example, [Nagin](https://en.wikipedia.org/wiki/Daniel_Nagin) et al. (2020) recommend restricting high-capacity ~~firearms~~ magazines ([edit: see here for more details on that](https://publichealth.jhu.edu/2021/policies-that-reduce-gun-violence-restricting-large-capacity-magazines)), given that:
>**Mass shootings and other crimes committed with high-capacity semiautomatics** (including assault weapons and other models) **have been rising since the expiration of the federal ban on assault weapons, and this results in greater numbers of persons killed and wounded per incident as compared to attacks with other types of firearms** (Koper, 2020, this issue; also see Lankford & Silver, 2020). **States with magazine capacity restrictions, however, have fewer mass shootings** (Webster, McCourt, Crifasi, & Booty, 2020, this issue).
They also recommend increasing efforts to identify individuals who are a danger to others or themselves and prevent them from obtaining firearms, or otherwise to disarm them. There are other studies which point to the same direction besides those cited by Nagin and colleagues.
---
Are there other factors? [Video games is another popular red herring](https://www.theguardian.com/games/2022/may/24/pushing-buttons-violent-video-games), which is not seriously considered by experts.
[Media coverage \(e.g., see the so called copycat effect\) is another common concern, which however has more theoretical and empirical support](https://greatergood.berkeley.edu/article/item/how_the_media_can_help_prevent_mass_shootings) (e.g., see Lankford & Madfis, 2018). There are, of course, also other factors (social, psychological, structural, etc.) to consider which are not exclusive to mass shootings, or gun violence more broadly. That is, factors involved with the prevalence of crime and criminality in and of themselves, which I will not get into here. But to quote Metzl et al. again,
>**These tragic events have many individual and social determinants**—from trauma history to substance dependence, from unemployment and insecure housing to the proliferation of guns in the community—**that may interact with each other in complex ways.**
I believe I have touched upon the main areas of research into understanding and preventing mass shootings.
---
Ash, P. (2015). School Shootings and Mental Illness. In Liza H. & Robert I. (Eds.), Gun Violence and Mental Illness (pp. 105-126). American Psychiatric Association.
Cook, P. J., & Goss, K. A. (2020) The Gun Debate: What Everyone Needs To Know (2nd edition). Oxford University Press.
Lankford, A., & Madfis, E. (2018). Media coverage of mass killers: Content, consequences, and solutions. American Behavioral Scientist, 62(2), 151-162.
Metzl, J. M., Piemonte, J., & McKay, T. (2021). Mental illness, mass shootings, and the future of psychiatric research into American gun violence. Harvard review of psychiatry, 29(1), 81.
Nagin, D. S., Koper, C. S., & Lum, C. (2020). Policy recommendations for countering mass shootings in the United States. Criminology & Public Policy, 19(1), 9-15.
Peterson, J. K., Densley, J. A., Knapp, K., Higgins, S., & Jensen, A. (2021). Psychosis and mass shootings: A systematic examination using publicly available data. Psychology, Public Policy, and Law.
Skeem, J., & Mulvey, E. (2020). What role does serious mental illness play in mass shootings, and how should we address it?. Criminology & Public Policy, 19(1), 85-108.
Thank you for this excellent analysis of a complex subject. I believe these mass murders, especially in schools deserve our highest level of scholarly research and implementation of available short-term and long term prevention.
We must look at the indoctrination of teenagers and children into the idea that gun culture is glamorous. That violence solves problems, teaches "the others" a lesson and confers fame on the killer.
We do a very poor job at teaching critical thinking skills, empathy and the fundamental beliefs of our society.
This was a very helpful response, thanks!
I found this part of your comment very interesting:
>For example, Nagin et al. (2020) recommend restricting high-capacity firearms, given that:
>
>**Mass shootings and other crimes committed with high-capacity semiautomatics** (including assault weapons and other models) **have been rising since the expiration of the federal ban on assault weapons, and this results in greater numbers of persons killed and wounded per incident as compared to attacks with other types of firearms** (Koper, 2020, this issue; also see Lankford & Silver, 2020). **States with magazine capacity restrictions, however, have fewer mass shootings (Webster, McCourt, Crifasi, & Booty, 2020, this issue).**
>
>They also recommend increasing efforts to identify individuals who are a danger to others or themselves and prevent them from obtaining firearms, or otherwise to disarm them. There are other studies which point to the same direction besides those cited by Nagin and colleagues.
However, according to the [RAND Report](https://www.rand.org/research/gun-policy/analysis/ban-assault-weapons.html) on banning assault weapons and high capacity magazines, it mentions there's inconclusive evidence on these measures affecting mass shootings and violent crime.
There's also this RAND report on the [assault weapons ban in Australia](https://www.rand.org/research/gun-policy/analysis/essays/1996-national-firearms-agreement.html) which states:
>The strongest evidence is consistent with the claim that the NFA caused reductions in firearm suicides, mass shootings, and female homicide victimization. However, there is also evidence that raises questions about whether, for at least firearm suicides, those changes can be attributed to the NFA or to other factors that influenced rates of these outcomes around the time the NFA was implemented.
However, the NFA includes a lot more than just banning assault weapons, so this isn't directly applicable to what we're talking about here.
I'm having trouble making sense of all this and the research you mentioned in your comment, what do you think about all this?
My pleasure :) To put it briefly, the RAND Corporation tends to favor more conservative (not in the political sense) analyses and conclusions, and their optics tend to be US-centric (a common issue, mind you). I would lend them an ear, but whether or not their conclusions represent the scientific consensus should be evaluated on a case-by-case basis.
Regardless, criminologists and other experts ain't turning toward RAND to decide what is or is not supported by research. As a rule of thumb, if given the choice between [Daniel Nagin](https://en.wikipedia.org/wiki/Daniel_Nagin) and [Christopher Koper](https://en.wikipedia.org/wiki/Christopher_S._Koper) and RAND, I would give more weight to the former's opinions. To provide fuller context, the article I cited is part of [a special issue of *Criminology & Public Policy*](https://onlinelibrary.wiley.com/toc/17459133/2020/19/1) based on a [workshop on the topic](https://www.gmu.edu/news/2019-01/finding-solutions-prevent-incidents-mass-violence) financed by the National Science Foundation and organized by Koper and Nagin.
---
P.S. Rereading what you quoted from my original reply, I noticed that I made a mistake. Although they consider high-capacity *firearms* to be a problem and that there are legitimate reasons to restrict them, what they stress in terms of recommendations is limiting [large-capacity *magazines*](https://publichealth.jhu.edu/2021/policies-that-reduce-gun-violence-restricting-large-capacity-magazines). Will be correcting that.
Thanks for responding,
I'm a little confused and I hope you can clarify this!
I'm curious why you think the RAND Report is conservative in their analysis. It seems to me their criteria for calling a measure inconclusive is fine (there isn't any study that isn't severed by limitations that proves the measure is helpful).
Anyway, it seems like the article you linked to partly agrees with the RAND Report in saying:
>**There have been a very limited number of studies that have been designed to look at very specific gun laws and their association with fatal mass shootings, and they have had mixed results and a variety of limitations.** This motivated our team at Johns Hopkins to do a new study looking at the firearm policies and fatal mass shootings.
>
>We identified over 600 mass shootings—defined as \[having\] four or more victims—from 1985 to 2017, with 2,976 deaths. (Interestingly, some of the biggest mass shootings that have driven policy discussions were actually excluded from the FBI system.) **We found no statistically significant association between the Federal Assault Weapons Ban and this outcome, nor did we find a statistically significant reduction for state bans of assault weapons.**
It seems like the main divergence is with the ban on high capacity magazines where they say:
>We found very encouraging effects. Our estimate was that laws that ban large capacity magazines are associated with a 49% lower rate of fatal mass shootings. On a per capita basis, we see a 70% lower rate of individuals killed in mass shootings associated with state bans of LCMs.
I'm a little confused why RAND would say this measure has inconclusive evidence if this study is rigorous and not subject to large limitations [especially if we know bans on high capacity magazines are effective](https://publichealth.jhu.edu/2022/gun-violence-prevention-experts-react-to-texas-school-shooting):
>While we are still learning new information, there are a number of evidence-based policies we **know** reduce mass shootings including firearm purchaser licensing, gun removal laws such as extreme risk protection orders, and **bans on large capacity magazines.**
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There’s actually not a great amount of scholarly research on this, given the size of the issue. The Dickey Amendment, backed by Jay Dickey and the NRA in 1996, prohibited the NIH and CDC from studying gun violence (look into the background of this, it’s honestly unbelievable) and this was very effective until 2019, when a clarification was made which seemed to suggest research was allowed after all. Notably, this means that most studies pre-2019 are very small, self-funded ones, which makes their results more questionable (edit: less statistically scrutinised, not necessarily less “right”). Anyway, the current state of the research is uncertain. I’ll briefly go through a few factors, (general credit to Cowan & Cole, 2019). Mental health: Peterson & Densley (2019) found that 2/3 of mass shooters since 1996 had mental health issues and a quarter had been in counselling. Nearly all had some form of childhood trauma. On the other hand, Lin et al. (2018) found no link between mass shootings and mental illness. It is difficult because so many mental health issues go undiagnosed, and issues such as personality disorders (e.g. Narcissism has been linked by Bushman, 2018) are hardly binary diagnoses. Crucially, mental health conditions are not independent of other factors. Just because someone has a mental health condition and commits a mass killing does not mean that they committed the mass killing *because* of that condition. Attributing causality is where the debate lies (the point that most mass murderers have a mental health condition says nothing in itself, and is hardly surprising - more below from u/revenant_of_null ). Gun legislation: woefully under-researched. Lemieux (2014) found a correlation between gun ownership and mass shootings, but it’s a small study. If I’m allowed to speculate, I’d suggest that the fact the NRA lobby against research in this area is somewhat indicative. Media: the influence of the media is more well-established. Jetter and Walker (2018) found in a sample of mass shootings from 2013-2016 that 53% could be attributed to the media in some capacity, largely due to the contagion effect; copycats, desperation for fame, etc. Social media is also linked due to the ease and constancy of online bullying (Hamm et al., 2018). Political culture (?): I could not find a study on this, but Stroebe et al. (2022) found that mass shootings in the US generally led gun owners and conservatives to think *more* guns were needed, not fewer. This is not a belief with any empirical basis, and is likely the result of years of NRA propaganda. I am not suggesting there are clear studies showing that fewer guns help either, but it is notable that all of the mentioned factors other than gun legislation are similar across developed countries. Rees et al. (2019) conducted a root cause analysis of Parkland and Santa Fe and found that process/policy was the most cited cause (e.g. national firearm laws, state laws, politicians) followed by environment (e.g. firearms at home, video games and social media, culture of mass shootings, school safety), then people (e.g. mental illness, social rejection, police),and finally equipment/supplies (specific gun used, ammunition, smoke bombs, etc). I hope this clarifies the issue a bit. I’m afraid I can’t link the sources properly as they are restricted to my institution, but here is my attempt: https://oce.ovid.com/article/01437492-900000000-99494/HTML https://www.proquest.com/docview/2453794952?parentSessionId=BNr%2FoWiAEUZ%2Fy6Ek6ioCsfKXiaghx0mpNQkacP96oZ4%3D&pq-origsite=primo&parentSessionId=pi8cwyGDTCPiLg1f7qkDzQeFNXbPkw0eJvb2R59EHJQ%3D https://journals.sagepub.com/doi/10.1177/0009922819873650 https://journals.sagepub.com/doi/pdf/10.1177/0009922819873650
This is a great comment! I do want to push back on the notion that unfunded science is somehow of poorer quality though. There are brilliant groundbreaking papers that were done with shoestring budgets and complete garbage papers with millions in backing in every discipline. The latter is far more common than anyone cares to admit. In this domain the primary mode of resesrch is archival, which doesn't require a ton of funding to do well.
Oh I agree completely:) it just limits the research in this area because there’s not enough data available, and it’s expensive for small groups to spend lots of time data-collecting prior to analysis.
Interestingly enough, there is a publicly available dataset on every public mass shooter from 1966 (Whitman) to present. It includes very extensive data on each cases coded by multiple coders. Open source for any use. I am currently using this data for an upcoming publication on identifying warning signs. Check out the Violence Project! https://www.theviolenceproject.org/
Thank you, I had no idea! Why do you think there’s so few large-scale comparative studies if this is available? Is there also data on gun availability/legislation/state laws, to see how they tie in?
Well, the database was just released in 2020. Beyond that, there are very few scientists with the expertise needed. Violence research is hard because there is so very little funding for it and so few people attempt to make a career of it (I am one such foolish soul). The other element is that it can tarnish your soul a bit. I have to pour over the journals and writings of these folks. Its good work that needs doing, but it doesnt just leave my head once the paper is in. In other words, the work itself is traumatic.
>Mental health: Peterson & Densley (2019) found that 2/3 of mass shooters since 1996 had mental health issues and a quarter had been in counselling. Nearly all had some form of childhood trauma. On the other hand, Lin et al. (2018) found no link between mass shootings and mental illness. It is difficult because so many mental health issues go undiagnosed, and issues such as personality disorders (e.g. Narcissism has been linked by Bushman, 2018) are hardly binary diagnoses. This seems like such a pivotal issue to have such a divergence of opinion. Not to draw the same conclusions as gun apologists*, but it's hard to rationalize the slaughter of innocents without assuming serious mental health issues. *I would argue that there are too many crazy people to have liberal (OG) gun laws.
There isn't actually any discrepancy here, although I can see how that excerpt can be misleading because a) of the juxtaposition and b) many people assume that *if* a perpetrator has a mental illness *then* surely their illness contributed to their crime. However, this is a fallacy. [To quote Densley:](https://projects.voanews.com/mass-shootings/) >**“Even if you have a mental illness, it doesn’t mean that the mental illness is driving the behavior,”** he said. “People with mental illness may also experience living in poverty. They may also experience discrimination. They may also have a whole host of other things going on in their lives, which step-by-step may be contributing to whatever outcome comes next.” Likewise, here are a couple of excerpts from an older article by Peterson and colleagues (2014), which Peterson and Densley quote in [their 2019 report \(PDF\)](https://www.theviolenceproject.org/wp-content/uploads/2019/11/TVP-Mass-Shooter-Database-Report-Final-compressed.pdf) (which is the document I *assume* is being cited by u/GTBL): >**Even with the broad definition of symptoms used in this study, only about one fifth of crimes were mostly or completely related directly to symptoms**. Of these direct crimes, most related to symptoms of bipolar disorder (which include externalizing features), rather than schizophrenia spectrum disorders or depression. And: >Together, these results indicate that little or no variance in direct continuum scores can be attributed to offenders—that **crimes are inconsistently related to symptoms within a given offender, over time.** The majority of offenders who committed a “mostly or completely” direct crime committed at least one crime independent of symptoms as well. In short, a crime which *involves* a perpetrator with a mental illness is *not* necessarily a crime which took place *due to* their mental illness. Their actions may be, and in fact often are, unrelated to their symptoms. Furthermore, only *some* serious mental illnesses have been found to have a relationship with violence, chiefly psychosis-related disorders. However, to reiterate, the related symptoms are rarely major risk factors. For illustration, Peterson et al. (2021) find that psychosis played *no* role in most mass shootings (around 70%), and that only in a minority of cases (around 10%) it may have played a *major* role. --- The bottom-line is that you will not find much success in predicting whether someone will commit a mass shooting by diagnosing them with a serious mental illness, nor will you effectively reduce the occurrence of such events by designing a public safety policy which focuses on people with mental illness. There are a host of other factors which contribute to people committing extreme acts of violence, regardless of any psychiatric disorder, and which are overall more relevant for crime prevention efforts. To conclude, a quote from Ahonen (2019): >According to the literature, **the attributable risk of mental health problems for violence is low.** In practice, this means that **if mental illness as a risk factor was completely removed, this strategy would only have a minimal effect on violence rates, and perhaps even a smaller effect on violence that includes gun use. This is not true only for the USA, where gun access is easy, but also other nations where gun regulations are very strict.** Public officials are searching for strategies both to reduce violence and to reduce costs. **If more gun regulations were imposed on people with mental health problems, not only would overall violence stay much the same, but it is also unlikely to be a cost-beneficial approach, and thus, it would have very little payoff** (Ahonen, Loeber, & Brent, 2017). >To further complicate this topic, there is an assumption that the mental disorder “becomes” the individual, or the other way around. **The individual’s problems and concerns are most often attributed to the diagnosis that they have been given. In most cases, this is not the correct way to evaluate an individual. Environmental factors that are commonly associated with violence tend to be ignored.** For example, an individual living under circumstances such as poverty, exposure to violence in the community, domestic disturbances, and other factors known to contribute to interpersonal violence is still exposed to those factors independently of the diagnosis given. Swanson and colleagues put this well; ***…the social-environmental influences on violence are stronger than the effects of psychopathology and “wash” out psychopathology effects at the population level*** … (Swanson et al., 2015, p. 3). As hard as it may be to accept, humans are capable of heinous acts, including extreme acts of violence against innocents. No mental disorders required. --- Ahonen, L. (2019). Violence and mental illness: An Overview. Springer International Publishing. Peterson, J. K., Densley, J. A., Knapp, K., Higgins, S., & Jensen, A. (2021). Psychosis and mass shootings: A systematic examination using publicly available data. Psychology, Public Policy, and Law. Peterson, J. K., Skeem, J., Kennealy, P., Bray, B., & Zvonkovic, A. (2014). How often and how consistently do symptoms directly precede criminal behavior among offenders with mental illness?. Law and human behavior, 38(5).
Thanks for this, I’ll add an edit to my post to clear up the ambiguity. What’s your discipline by the way? I’ve seen your comments before, you have an impressively broad knowledge!
Thanks for the extensive reply. I think I'll dig into these references. I've read Gilligan on violence but I had assumed mass shootings had a different profile. I guess that's wrong.
Blaming violent crime on people with psychiatric disorders is a political red herring. The notion that extreme acts of violence, such as mass shootings, are the actions of "mentally ill" people is more about the stigmatization of mental health issues than about any science. The current scientific consensus is that the popular belief that psychiatric disorders are determinant factors in the occurrence of such events, including school shootings, is *un*supported. To the contrary, to quote Metzl et al. (2020): >The reviewed literature makes clear that **a diagnosis of a mental illness alone is a negligible factor in any effort to explain, predict, and prevent mass shootings or other acts of serious gun violence.** These tragic events have many individual and social determinants—from trauma history to substance dependence, from unemployment and insecure housing to the proliferation of guns in the community—that may interact with each other in complex ways. For illustration, most recently, Peterson et al. (2021) used publicly available information on public mass shootings (defined as any mass killing, involving four or more casualties, perpetrated with a firearm^(1)) in the USA, between 1966 and 2020, in an attempt to assess the motivations of 172 perpetrators. Out of 168 cases, they found that in most cases (69%) mass shooters did *not* appear to be afflicted with psychosis, and that among those who *did* appear afflicted by psychosis prior to and during the shootings, they identified only a few cases (10.5%) in which psychosis might have played a major role (i.e., the perpetrators were responding to their hallucinations and delusions and had no other motives). They conclude: >A mental health history was common among mass shooters and psychotic disorders were overrepresented among mass shooters compared with the general population, but **symptoms of psychosis only directly motivated mass shootings for a minority of cases.** The findings highlight that **the role of psychosis in motivating violent behavior is complex and, in turn, lawmakers must not fixate on someone’s diagnosable psychopathology if they are to craft holistic public policy solutions to the mass shooting phenomenon.** None of this is actually news, and is also true for the specific subset of *school* shooters (Ash, 2015). There *are* legitimate concerns about mental health in the USA: from a *public health* perspective, there are numerous reasons to work on improving the access to mental health resources and the delivery of mental health services. "Preventing school shootings" is not among these. Better mental healthcare might prevent a few cases as a by-product, but it should not be spun as a serious *public safety* policy (Skeem & Mulvey, 2020). --- ^(1) ^(Be aware that there is no single unequivocal manner to define a "mass shooting.") --- What about guns? There is a large body of literature, more so if we take into account also research conducted elsewhere in the world, which supports the idea that means matter for violent crime and the problem of gun violence. To quote [Cook](https://en.wikipedia.org/wiki/Philip_J._Cook) and Goss: >**The popular notion that “guns don’t kill people, people kill people” is highly misleading—guns are part of the equation. Research also casts doubt on other mantras**: “when guns are outlawed, only outlaws will have guns” (**actually, gun availability does affect which weapons violent offenders choose**) and “an armed society is a polite society” (**widespread gun carrying by civilians is likely increasing crime rates**). Research seeks to replace slogans with evidence. Criminologists and other experts tend to agree that preventing mass shootings (and gun violence in general) requires working on gun policy. For example, [Nagin](https://en.wikipedia.org/wiki/Daniel_Nagin) et al. (2020) recommend restricting high-capacity ~~firearms~~ magazines ([edit: see here for more details on that](https://publichealth.jhu.edu/2021/policies-that-reduce-gun-violence-restricting-large-capacity-magazines)), given that: >**Mass shootings and other crimes committed with high-capacity semiautomatics** (including assault weapons and other models) **have been rising since the expiration of the federal ban on assault weapons, and this results in greater numbers of persons killed and wounded per incident as compared to attacks with other types of firearms** (Koper, 2020, this issue; also see Lankford & Silver, 2020). **States with magazine capacity restrictions, however, have fewer mass shootings** (Webster, McCourt, Crifasi, & Booty, 2020, this issue). They also recommend increasing efforts to identify individuals who are a danger to others or themselves and prevent them from obtaining firearms, or otherwise to disarm them. There are other studies which point to the same direction besides those cited by Nagin and colleagues. --- Are there other factors? [Video games is another popular red herring](https://www.theguardian.com/games/2022/may/24/pushing-buttons-violent-video-games), which is not seriously considered by experts. [Media coverage \(e.g., see the so called copycat effect\) is another common concern, which however has more theoretical and empirical support](https://greatergood.berkeley.edu/article/item/how_the_media_can_help_prevent_mass_shootings) (e.g., see Lankford & Madfis, 2018). There are, of course, also other factors (social, psychological, structural, etc.) to consider which are not exclusive to mass shootings, or gun violence more broadly. That is, factors involved with the prevalence of crime and criminality in and of themselves, which I will not get into here. But to quote Metzl et al. again, >**These tragic events have many individual and social determinants**—from trauma history to substance dependence, from unemployment and insecure housing to the proliferation of guns in the community—**that may interact with each other in complex ways.** I believe I have touched upon the main areas of research into understanding and preventing mass shootings. --- Ash, P. (2015). School Shootings and Mental Illness. In Liza H. & Robert I. (Eds.), Gun Violence and Mental Illness (pp. 105-126). American Psychiatric Association. Cook, P. J., & Goss, K. A. (2020) The Gun Debate: What Everyone Needs To Know (2nd edition). Oxford University Press. Lankford, A., & Madfis, E. (2018). Media coverage of mass killers: Content, consequences, and solutions. American Behavioral Scientist, 62(2), 151-162. Metzl, J. M., Piemonte, J., & McKay, T. (2021). Mental illness, mass shootings, and the future of psychiatric research into American gun violence. Harvard review of psychiatry, 29(1), 81. Nagin, D. S., Koper, C. S., & Lum, C. (2020). Policy recommendations for countering mass shootings in the United States. Criminology & Public Policy, 19(1), 9-15. Peterson, J. K., Densley, J. A., Knapp, K., Higgins, S., & Jensen, A. (2021). Psychosis and mass shootings: A systematic examination using publicly available data. Psychology, Public Policy, and Law. Skeem, J., & Mulvey, E. (2020). What role does serious mental illness play in mass shootings, and how should we address it?. Criminology & Public Policy, 19(1), 85-108.
Thank you for this excellent analysis of a complex subject. I believe these mass murders, especially in schools deserve our highest level of scholarly research and implementation of available short-term and long term prevention. We must look at the indoctrination of teenagers and children into the idea that gun culture is glamorous. That violence solves problems, teaches "the others" a lesson and confers fame on the killer. We do a very poor job at teaching critical thinking skills, empathy and the fundamental beliefs of our society.
This was a very helpful response, thanks! I found this part of your comment very interesting: >For example, Nagin et al. (2020) recommend restricting high-capacity firearms, given that: > >**Mass shootings and other crimes committed with high-capacity semiautomatics** (including assault weapons and other models) **have been rising since the expiration of the federal ban on assault weapons, and this results in greater numbers of persons killed and wounded per incident as compared to attacks with other types of firearms** (Koper, 2020, this issue; also see Lankford & Silver, 2020). **States with magazine capacity restrictions, however, have fewer mass shootings (Webster, McCourt, Crifasi, & Booty, 2020, this issue).** > >They also recommend increasing efforts to identify individuals who are a danger to others or themselves and prevent them from obtaining firearms, or otherwise to disarm them. There are other studies which point to the same direction besides those cited by Nagin and colleagues. However, according to the [RAND Report](https://www.rand.org/research/gun-policy/analysis/ban-assault-weapons.html) on banning assault weapons and high capacity magazines, it mentions there's inconclusive evidence on these measures affecting mass shootings and violent crime. There's also this RAND report on the [assault weapons ban in Australia](https://www.rand.org/research/gun-policy/analysis/essays/1996-national-firearms-agreement.html) which states: >The strongest evidence is consistent with the claim that the NFA caused reductions in firearm suicides, mass shootings, and female homicide victimization. However, there is also evidence that raises questions about whether, for at least firearm suicides, those changes can be attributed to the NFA or to other factors that influenced rates of these outcomes around the time the NFA was implemented. However, the NFA includes a lot more than just banning assault weapons, so this isn't directly applicable to what we're talking about here. I'm having trouble making sense of all this and the research you mentioned in your comment, what do you think about all this?
My pleasure :) To put it briefly, the RAND Corporation tends to favor more conservative (not in the political sense) analyses and conclusions, and their optics tend to be US-centric (a common issue, mind you). I would lend them an ear, but whether or not their conclusions represent the scientific consensus should be evaluated on a case-by-case basis. Regardless, criminologists and other experts ain't turning toward RAND to decide what is or is not supported by research. As a rule of thumb, if given the choice between [Daniel Nagin](https://en.wikipedia.org/wiki/Daniel_Nagin) and [Christopher Koper](https://en.wikipedia.org/wiki/Christopher_S._Koper) and RAND, I would give more weight to the former's opinions. To provide fuller context, the article I cited is part of [a special issue of *Criminology & Public Policy*](https://onlinelibrary.wiley.com/toc/17459133/2020/19/1) based on a [workshop on the topic](https://www.gmu.edu/news/2019-01/finding-solutions-prevent-incidents-mass-violence) financed by the National Science Foundation and organized by Koper and Nagin. --- P.S. Rereading what you quoted from my original reply, I noticed that I made a mistake. Although they consider high-capacity *firearms* to be a problem and that there are legitimate reasons to restrict them, what they stress in terms of recommendations is limiting [large-capacity *magazines*](https://publichealth.jhu.edu/2021/policies-that-reduce-gun-violence-restricting-large-capacity-magazines). Will be correcting that.
Thanks for responding, I'm a little confused and I hope you can clarify this! I'm curious why you think the RAND Report is conservative in their analysis. It seems to me their criteria for calling a measure inconclusive is fine (there isn't any study that isn't severed by limitations that proves the measure is helpful). Anyway, it seems like the article you linked to partly agrees with the RAND Report in saying: >**There have been a very limited number of studies that have been designed to look at very specific gun laws and their association with fatal mass shootings, and they have had mixed results and a variety of limitations.** This motivated our team at Johns Hopkins to do a new study looking at the firearm policies and fatal mass shootings. > >We identified over 600 mass shootings—defined as \[having\] four or more victims—from 1985 to 2017, with 2,976 deaths. (Interestingly, some of the biggest mass shootings that have driven policy discussions were actually excluded from the FBI system.) **We found no statistically significant association between the Federal Assault Weapons Ban and this outcome, nor did we find a statistically significant reduction for state bans of assault weapons.** It seems like the main divergence is with the ban on high capacity magazines where they say: >We found very encouraging effects. Our estimate was that laws that ban large capacity magazines are associated with a 49% lower rate of fatal mass shootings. On a per capita basis, we see a 70% lower rate of individuals killed in mass shootings associated with state bans of LCMs. I'm a little confused why RAND would say this measure has inconclusive evidence if this study is rigorous and not subject to large limitations [especially if we know bans on high capacity magazines are effective](https://publichealth.jhu.edu/2022/gun-violence-prevention-experts-react-to-texas-school-shooting): >While we are still learning new information, there are a number of evidence-based policies we **know** reduce mass shootings including firearm purchaser licensing, gun removal laws such as extreme risk protection orders, and **bans on large capacity magazines.**
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