When Do Delusions Lead to Violence?

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In the public imagination, there’s a tight link between violence and certain forms of highly visible mental illness involving delusions and hallucinations. Researchers and advocates for the mentally ill have been trying to push back against this notion for a while, arguing that research doesn’t support it — a task made more difficult by those instances, like Adam Lanza’s Sandy Hook rampage, in which a person who appears to have serious mental illness does commit a heinous act of violence. A recent study, though, adds a bit of much-needed nuance to this issue.

In research published in Clinical Psychological Science, a team led by Jennifer Skeem of UC Berkeley’s School of Social Welfare used a preexisting database to identify 305 instances of violence committed by 100 people who had some history of inpatient psychological treatment. They were specifically curious as to how frequently these incidents were immediately preceded by an episode of psychosis — a dramatic, debilitating break from reality — on the part of the perpetrator.

As it turned out, just 12 percent of the incidents were immediately preceded by psychosis, which means that even in a group of people already identified as being both mentally ill and violent, it just isn’t that common for someone to “snap” and start hurting people in a delusional state. “These findings suggest that psychosis sometimes foreshadows violence for a fraction of high-risk individuals,” the authors write, “but violence prevention efforts should also target factors like anger and social deviance.”

The researchers also uncovered some potentially important categories within the population they studied:

Together, our findings suggest that a broad distinction may be made between individuals with exclusively non-psychosis-preceded violence and individuals with a mixture of psychosis-preceded and non-psychosis preceded violence. There is little evidence for a subgroup with exclusively psychosis-preceded violence.

In other words, there don’t really appear to be people, in this sample, at least, who only commit violence as the result of a psychotic break — other violence-predicting factors are present as well, and they can help researchers identify who might actually be a risk to others. And, more broadly, it bears frequent repeating that mentally ill people are more likely to be targeted by violence than to perpetrate it.