Large epidemiologic studies show that psychiatric illness is a risk factor for violent behavior, but the risk is small and linked only to a few serious mental disorders. People with schizophrenia, major depression or bipolar disorder were two to three times as likely as those without these disorders to be violent. The actual lifetime prevalence of violence among people with serious mental illness is about 16 percent compared with 7 percent among people who are not mentally ill.

What most people don’t know is that drug and alcohol abuse are far more powerful risk factors for violence than other psychiatric illnesses. Individuals who abuse drugs or alcohol but have no other psychiatric disorder are almost seven times more likely than those without substance abuse to act violently.

As a psychiatrist, I welcome calls from our politicians to improve our mental health care system. But even the best mental health care is unlikely to prevent these tragedies.

If we can’t reliably identify people who are at risk of committing violent acts, then how can we possibly prevent guns from falling into the hands of those who are likely to kill?