Although it is believed that mental health factors significantly in most mass murders and mass shootings, new findings published in the journal Psychological Medicine suggest that isn’t the case. In fact, serious mental illness is present only in 11% of mass murderers and 8% of mass shooters, according to a news release from the Columbia University Department of Psychiatry in New York City.

For their investigation, researchers from Columbia and the New York State Psychiatric Institute analyzed 1,315 mass murders of all types from around the world in hopes of better understanding mass shootings.

Research showed that people who committed mass murders by fire, explosives, stabbing and other means had a prevalence of serious mental illness of 18%. Although almost two thirds of mass murders are committed with guns, those that don’t involve firearms resulted in significantly more casualties.

Investigators determined that mass shooters in the United States were more likely to have a history of crime, use recreational drugs, misuse alcohol and have a history of nonpsychotic psychiatric or neurologic symptoms.

In addition, findings revealed that most mass shooters use nonautomatic firearms. Individuals with psychiatric or neurologic conditions were more likely to choose semiautomatic weapons than nonautomatic ones.

This particular finding could have implications for how background checks for the purchase of weapons are conducted.

"The findings from this potentially definitive study suggest that emphasis on serious mental illness, such as schizophrenia or psychotic mood disorders, as a risk factor for mass shootings is given undue emphasis, leading to public fear and stigmatization,” said Gary Brucato, PhD, the assistant director of the Center of Prevention and Evaluation at Columbia and one of the study’s lead researchers.

Instead, researchers believe that other factors play a more apparent role in mass shootings, including legal problems, substance and alcohol use and difficulty coping with life events. This is why prevention and policy efforts should focus on these areas rather than serious mental illness, concludes Paul S. Appelbaum, MD, a professor at Columbia and a study coauthor.

For related coverage, read “Mental Health Issues Aren’t the Main Driver of Violence Toward Others.”