But mental illness is not a major feature of mass killers: Only about a quarter of mass shooters have a diagnosed mental illness, and the illness might not necessarily be related to their crime. Of that quarter, about 75% of mass shooters had a mood disorder, 25% had an anxiety disorder,19% had psychosis, and 1% had the developmental condition, such as autism spectrum disorder.
Yet, as mass shootings have dramatically increased, mental illness has become inextricably associated with these events in the media and popular opinion, Dr. Rosenbaum said. There have been 74 school shootings since the Newtown, Conn., tragedy, and mental illness is repeatedly brought up as a contributor, she said.
A 2014 study that analyzed 25% of a random sample of news stories from 1997 to 2012 on serious mental illness and gun violence (before Newtown) found that most of the coverage occurred after mass shootings and “ ‘dangerous people’ with serious mental illness were more likely to be mentioned than ‘dangerous weapons’ as a cause of gun violence” (Am J Public Health. 2014 Mar;104[3]:406-13).
Dr. Karen B. Rosenbaum
Yet this association does not reflect reality, Dr. Rosenbaum said. One meta-analysis found that prevention of one stranger homicide by someone with psychosis would require detaining 35,000 people with schizophrenia who had been judged as being at high risk for violence (Schizophr Bull. 2011 May;37[3]:572-9).
Further, the relationship between violence and mental illness is not simple. Complex historical factors are usually involved, including past violence, juvenile detection, physical abuse, substance abuse, age, parental arrest record, and life circumstances – such as a recent divorce, unemployment, or victimization.
The greater danger of a person with mental illness is the harm they will do to themselves, research shows. A study of 255 recently discharged psychiatric patients and 490 matched community residents found that the patients were no more likely to perpetuate violence than were the community members, but they were significantly more likely to report being suicidal (Int J Law Psychiatry. 2018 Jan-Feb;56:44-9).
Rather than mental illness, what is associated with violence is substance use and access to weapons, Dr. Rosenbaum said.
“The United States is one of only three countries in the world with a constitutionally protected right to own firearms,” Dr. Rosenbaum said, citing a 2017 study by John S. Rozel, MD, and Edward P. Mulvey, PhD, (Annu Rev Clin Psychol. 2017 May 8;13:445-9). And the United States has few restrictions on that right. With more than 350 million privately owned firearms – approximately 30% of all privately owned firearms in the world – the U.S. population exceeds all other countries in both per capita and absolute gun ownership.
And research shows that guns don’t make a country safer: Guns per capita are significantly correlated with firearm-related deaths; mental illness is only of borderline significance (Am J Med. 2013 Oct;126[10]:873-6).
Substance use – including use of cocaine, hallucinogens, methamphetamine, ecstasy, and prescription medications – has a stronger correlation with gun-carrying and gun-related behaviors (Inj Prev. 2017 Dec; 23[6]:383-7 and Epidemiol Rev. 2016;38[1]:46-61). Both acute and chronic alcohol misuse also are linked to firearm ownership and violence toward others and one’s self (Prev Med. 2015 Oct;79:15-21).
Yet public misperceptions of mental illness as a contributor to violence persists, research shows (Aust N Z J Psychiatry. 2014 Aug;48[8]:764-71), further stigmatizing people with psychiatric conditions and potentially reducing the likelihood of their seeking treatment. Politicians contribute to these misperceptions; an example is House Speaker Paul Ryan’s comment after the Parkland, Fla., school shooting: “Mental health is often a big problem underlying these tragedies.”
“The media sensationalizes violent crimes committed by people with mental illness, especially after mass shooting, and this societal bias contributes to the stigma that leads to decreased treatment seeking and discrimination,” Dr. Rosenbaum said, citing research from Mohit Varshney, MD, and his associates (J Epidemiol Community Health. 2016 Mar;70[3]:223-5). “It is important to dissociate the concept of mental illness from dangerousness.”