In light of the tragic shooting incident in Tucson, Arizona yesterday that left 18 people injured, including U.S. Congresswoman Gabrielle Gifford, and at least two people dead, including U.S. federal judge John Roll, it’s important to remember that, despite much casual discussion by the media about the influence of mental illness on individuals’ violent actions, the scientific evidence suggests mental illness does not correlate to interpersonal violence – as least not compared to other variables, especially drug and alcohol abuse.
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.