The assumption that mass murderers tend to suffer from severe psychological illness has contributed greatly to the stigma surrounding mental illness. However, the authors of a new study claim that this association is wide of the mark, as only around 11 percent of mass killers actually have a history of psychotic symptoms.
Published in the journal Psychological Medicine, the study draws on the Columbia Mass Murder Database, which includes details on 14,785 murders committed around the world between 1900 and 2019. Of these, 1,315 were identified as mass killings, accounting for a total of 10,877 deaths.
After analyzing the available information regarding the perpetrator of each crime, the study authors noted that only eight percent of mass shooters had been diagnosed with psychosis at any point in their lives. This figure rose to 18 percent for those who committed mass murder using means other than a firearm – such as explosives, arson, poisoning, stabbing, bludgeoning, or driving a vehicle into a crowd.
Since 1970, mass shootings have become far more common than other forms of mass murder worldwide, and represent around two-thirds of all mass killings in the database. According to the researchers, the majority of these shootings have occurred in the US, to the extent that "mass murder incidents outside of the USA [were] too infrequent to allow for a meaningful statistical comparison of methods with US cases."
Taking a closer look at the perpetrators of these firearm-related atrocities, the study authors found that while few exhibited psychotic tendencies, many had a history of legal problems, drug and alcohol use, and non-psychotic mental health issues such as anxiety or personality disorders.
Interestingly, those who experienced symptoms of non-psychotic neurologic or psychiatric illness were found to be more likely to use semi-automatic weapons, while shooters with no history of psychopathology used non-automatic firearms more often. No explanation for these trends is given, although the researchers point out that low rates of psychosis among mass shooters may be a consequence of the fact that people with mental health issues are generally less able to acquire guns.
In a statement, study author Dr Gary Brucato commented that "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."
Recognizing the limitations of this study, the authors concede that their database only contains media and police reports written in English, and therefore relates to murders committed by people from certain countries and cultures. Nonetheless, they conclude that a new approach may be needed in order to prevent further tragedies of this kind, explaining that “policies aimed at preventing mass shootings by focusing on serious mental illness, characterized by psychotic symptoms, may have limited impact.”
As an alternative, they suggest that “policies such as those targeting firearm access, recreational drug use and alcohol misuse, legal history, and non-psychotic psychopathology might yield more substantial results.”