Shortly after Jared Lee Loughner had been identified as the alleged shooter of Arizona Rep. Gabrielle Giffords, online sleuths turned up pages of rambling text and videos he had created. A wave of amateur diagnoses soon followed, most of which concluded that Loughner was not so much a political extremist as a man suffering from "paranoid schizophrenia."
For many, the investigation will stop there. No need to explore personal motives, out-of-control grievances or distorted political anger. The mere mention of mental illness is explanation enough. This presumed link between psychiatric disorders and violence has become so entrenched in the public consciousness that the entire weight of the medical evidence is unable to shift it. Severe mental illness, on its own, is not an explanation for violence, but don't expect to hear that from the media in the coming weeks.
Seena Fazel is an Oxford University psychiatrist who has led the most extensive scientific studies to date of the links between violence and two of the most serious psychiatric diagnoses—schizophrenia and bipolar disorder, either of which can lead to delusions, hallucinations, or some other loss of contact with reality. Rather than looking at individual cases, or even single studies, Fazel's team analyzed all the scientific findings they could find. As a result, they can say with confidence that psychiatric diagnoses tell us next to nothing about someone's propensity or motive for violence.
A 2009 analysis of nearly 20,000 individuals concluded that increased risk of violence was associated with drug and alcohol problems, regardless of whether the person had schizophrenia. Two similar analyses on bipolar patients showed, along similar lines, that the risk of violent crime is fractionally increased by the illness, while it goes up substantially among those who are dependent on intoxicating substances. In other words, it's likely that some of the people in your local bar are at greater risk of committing murder than your average person with mental illness.
http://www.slate.com/id/2280619/
