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Is It Guns or Mental Illness?

Will targeting mental illness stop mass shootings?

In order to prevent future tragedies like the three mass shootings last week which killed at least 32 people, we need to understand the real cause(s) and lawmakers need to be informed. This morning, the President said: “Mental illness and hatred pulls the trigger, not the gun.” He went on to call mass shooters “mentally ill monsters.” But how significant is mental illness in these horrible crimes, and how would those with mental illness be identified and stopped?

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Mental Illness

It depends on how you define it. Most people think of mental illness as a psychosis, such as schizophrenia, in which the person is out of touch with reality and has hallucinations and/or delusions.

Studies show that about 20-25% of mass shooters (defined as killing three or more in one incident) suffered from this type of mental illness. “About one in five are likely psychotic or delusional, according to Dr. Michael Stone, a forensic psychiatrist at Columbia University who maintains a database of 350 mass killers going back more than a century…. But the rest of these murderers do not have any severe, diagnosable disorder.” For example, two of the largest mass murders were committed by Omar Mateen at the Pulse nightclub in Orlando and Stephen Paddock in Las Vegas, who had no apparent history of mental illness before their mass murders. Dr. Stone says: “The majority of the killers were disgruntled workers or jilted lovers who were acting on a deep sense of injustice,” and not mentally ill.”1

J. Reid Meloy, a forensic psychologist who often consults with the F.B.I., identifies a “paranoid spectrum.” “At the extreme end is full-on psychosis of Loughner variety [who shot Congresswoman Gabby Giffords and killed six others in Tucson in 2011]. But the majority of people on this spectrum are not deeply ill; rather they are injustice collectors. They are prone to perceive insults and failures as cumulative, and often to blame them on one person or one group.”Ibid.

A Department of Justice analysis also found roughly 20 percent had a psychotic disorder. “The overall rate of any psychiatric history among mass killers—including such probable diagnoses as depression, learning disabilities or A.D.H.D.—was 48 percent.” Ibid.

In their chapter on “Mass Shootings and Mental Illness,” in the book, Gun Violence and Mental Illness, Dr. James Knoll and George Annas report that “The overall contribution of people with serious mental illness to violent crimes is only about 3%. When these crimes are examined in detail, an even smaller percentage of them are found to involve firearms.”2

Will Identifying Mental Illness Help?

Dr. Knoll and Mr. Annas state that laws focusing on screening out gun ownership for the mentally ill will not solve the problem of mass shootings. “Perpetrators of mass shootings are unlikely to have a history of involuntary psychiatric hospitalizations. Thus, databases intended to restrict access to guns and established by guns laws that broadly target people with mental illness will not capture this group of individuals.” Ibid.

Furthermore, a significant number of mass shooters are in their late teens to early 20s, when signs of severe mental illness may not yet be observable. For example, Jared Loughner, the Tucson shooter above, was just starting to show signs of schizophrenia, which are usually a tendency to become withdrawn and lose interest in activities—not violence. The diagnostic manual of the mental health professionals, currently the DSM-5, states: “The psychotic features of schizophrenia typically emerge between the late teens and the mid-30s.”3 Those with this disorder represent approximately 1% of the U.S. population, and only 3-5% of all violence, including gun violence, is due to such mental illness. Yet for those few who are violent, it is only “during certain high-risk periods, such as during a first episode of psychosis.”4 In other words, there may be no history of a tendency toward violence, even of severe mental illness, to find in a background check for these young adult shooters.

The DSM-5 identifies numerous other mental disorders which the average person usually does not identify with mental illness. For example, major depression is relatively common (studies show up to 7% of the U.S. population each year) and personality disorders are about 15% of the U.S. population. Yet these are mentioned sometimes with mass shootings. (Dr. Stone above thought traits of these may be present in about 10% of mass shootings.) At this point, we're talking about over twenty percent of the U.S. population as qualifying for a mental illness, without any unique correlation with gun violence.


In studies that compare the United States with other similar countries in terms of the number of mass shootings, the only major difference was not mental health, but the amount of guns. According to a 2015 study by Adam Lankford, a professor at the University of Alabama, “a country’s rate of gun ownership correlated with the odds that it would experience a mass shooting [and] mass shootings were better explained by a society’s access to guns than by its baseline level of violence.” With only 4.4 percent of the world’s population, Americans own 42 percent of the guns. Not surprisingly, America’s overall rate of gun homicides was 33 per million people, whereas Canada’s rate was 5 per million and Britain’s was 0.7 per million.5

Do we therefore have more crime? Apparently not. A 1999 study by Franklin Zimring and Gordon Hawkins found that we have similar levels of crime as other countries, such as Britain. But during a crime Americans are more likely to be killed. “A New Yorker is just as likely to be robbed as a Londoner, for instance, but the New Yorker is 54 times more likely to be killed in the process.” Ibid.

It’s not mental illness, it’s not more crime, it’s not more violence and it’s not even more video games (see PT blog by Art Markman). I think we have our answer: It’s access to guns that kills people.


1. Benedict Carey, “Are Mass Murderers Insane? Usually Not, Researchers Say,” The New York Times, Nov. 8, 2017.

2. James L. Knoll and George D. Annas, "Mass Shootings and Mental Illness," Gun Violence and Mental Illness, Liza H. Gold and Robert I. Simon, Eds, American Psychiatric Association: Arlington, VA (2016), 82.

3. American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA, American Psychiatric Association, 2013, 102.

4. Emma McGinty and Daniel Webster, "Gun Violence and Serious Mental Illness," Gun Violence and Mental Illness, Liza H. Gold and Robert I. Simon, Eds, American Psychiatric Association: Arlington, VA (2016), 3.

5. Max Fisher and Josh Keller, “What Explains U.S. Mass Shootings? International Comparisons Suggest an Answer,” New York Times, Nov. 7, 2017.

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