From “In Gun Debate, a Misguided Focus on Mental Illness,” Richard A. Friedman, M. D., NYT:
“But there is overwhelming epidemiological evidence that the vast majority of people with psychiatric disorders do not commit violent acts. Only about 4 percent of violence in the United States can be attributed to people with mental illness.
“This does not mean that mental illness is not a risk factor for violence. It is, but the risk is actually small. Only certain serious psychiatric illnesses are linked to an increased risk of violence.
“One of the largest studies, the National Institute of Metal Health’s Epidemiologic Catchment Area study, which followed nearly 18,000 subjects, found that the lifetime prevalence of violence among people with serious mental illness — like schizophrenia and bipolar disorder — was 16 percent, compared with 7 percent among people without any mental disorder. Anxiety disorders, in contrast, do not seem to increase the risk at all.
“Alcohol and drug abuse are far more likely to result in violent behavior than mental illness by itself. In the National Institute of Mental Health’s E.C.A. study, for example, people with no mental disorder who abused alcohol or drugs were nearly seven times as likely as those without substance abuse to commit violent acts.
“It’s possible that preventing people with schizophrenia, bipolar disorder and other serious mental illnesses from getting guns might decrease the risk of mass killings. Even the Supreme Court, which in 2008 strongly affirmed a broad right to bear arms, at the same time endorsed prohibitions on gun ownership ‘by felons and the mentally ill.’
“But mass killings are very rare events, and because people with mentally illness contribute so little to overall violence, these measures would have little impact on everyday firearm-related killings. Consider that between 2001 and 2010, there were nearly 120,000 gun-related homicides, according to the National Center for Health Statistics. Few were perpetrated by people with mental illness.
“Perhaps more significant, we are not very good at predicting who is likely to be dangerous in the future. According to Dr. Michael Stone, professor of clinical psychiatry at Columbia and an expert on mass murderers, ‘Most of these killers are young men who are not floridly psychotic. They tend to be paranoid loners who hold a grudge and are full of rage.’
“Even though we know from large-scale epidemiologic studies like the E.C.A. study that a young psychotic male who is intoxicated with alcohol and has a history of involuntary commitment is at a high risk of violence, most individuals who fit this profile are harmless.”