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Peter McKnight is an adjunct professor in the School of Criminology at Simon Fraser University

Consider the following scenario, which I have adapted from one provided by psychologist Vaughan Bell: Suppose a man stabs a stranger on the street. You ask me to explain his violent act, and I respond, "He was a hockey player."

You'd probably conclude that my "explanation" says more about my sorry mental state than about the mental state of the man in question. Sure, some hockey players are violent, but whatever does that have to do with his behaviour?

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Now, what if I instead said the man was mentally ill? Ah, now there's an explanation with teeth, an explanation that provides a complete understanding of the crime. Right?

It certainly seems right given how often mental illness is offered as an explanation for violent behaviour. Just this week, for example, we heard that the recent attack on a Canadian Forces recruiting centre might have been the result, not of terrorism, but of alleged assailant Ayanle Hassan Ali inheriting his mother's mental illness.

And virtually every news story has pointed to mental illness as the explanation for the alleged behaviour of Rohinie Bisesar, who stands accused of stabbing a woman to death in a Toronto Shoppers Drug Mart.

Given these stories, it's little wonder that studies show people who watch or read the news are more likely to avoid people living with mental illness and to view mental illness and violence as inexorably linked.

Scientific studies, however, suggest otherwise. Studies have identified numerous factors associated with violent behaviour, including sex, age, socioeconomic status, unemployment, victimization, and, especially, substance abuse. Indeed, a bad drunk presents a much greater threat to your bodily integrity than a schizophrenic.

A schizophrenic with a drinking problem can be dangerous, but that's primarily because of his alcohol use and not his mental illness. And that raises another point: Like anyone, a person living with mental illness can commit a violent act that is completely unrelated to the illness.

In fact, a 2014 study of mentally disordered offenders found that only 7.5 per cent of subjects' crimes were associated with their mental illnesses. In other words, just because someone attacks you doesn't mean she's crazy; she might just plain not like you.

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Now all of this said, studies have found a link between violence and some forms of serious mental illness such as schizophrenia. The difficulty is in determining what it is about schizophrenia that leads some sufferers to become violent.

In a recent study, researchers discovered an association between "positive" symptoms – hallucinations and delusions – and risk of violence. And the risk was greatest in cases involving "a network of systemized persecutory delusions."

In light of this, I should highlight two things: First, we ought to redouble our efforts to diagnose and treat serious mental illness, since schizophrenics receiving treatment are rarely dangerous. And second, violence is associated only with a small subgroup of untreated schizophrenics, not with all schizophrenics, let alone all people diagnosed with mental illness.

Perhaps I should highlight one more thing: As you hear more about Rohinie Bisesar and Ayanle Hassan Ali in the coming weeks, remember that the myths of mental illness do everyone far more harm than people living with mental illness ever could. Or would.

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