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States are also developing plans on gun control and mental health. New York has passed the first law in response to the Newtown school shootings. It requires mental health professionals to report patients they deem likely to harm themselves or someone else.
Still, as NPR's Jon Hamilton reports, researchers who study violence among the mentally ill think requirements like New York's won't help much.
JOHN HAMILTON, BYLINE: Researchers say one issue with laws like New York's is that they compel mental health professionals to report thousands of people who aren't at all likely to shoot someone.
Barry Rosenfeld is a psychologist at Fordham University in the Bronx.
BARRY ROSENFELD: With these laws we're destined to cast a very, very large net, put a lot of people under it, probably restrict a lot of people's behaviors unnecessarily, and maybe we'll prevent an incident or two. I hope.
HAMILTON: Or maybe not. Rosenfeld says a big problem is that, despite the attention they get, mass shootings are very rare events.
ROSENFELD: When you're trying to predict a rare event, it's really, really hard. And the more rare the event, the harder it is to accurately predict it and the greater your error rate is going to be when you label people as potentially dangerous. You're just going to capture lots and lots of non-dangerous people.
HAMILTON: Rosenfeld says another problem is that most mental health professionals don't have MDs or PhDs and haven't received much training in assessing a patient's risk of violence.
ROSENFELD: Even most typical psychiatrists and psychologists have relatively limited training in it. It's not a particularly substantial part of how we train mental health professionals.
HAMILTON: Rosenfeld is one of a small number of experts who are trained to assess the risk that a person will act violently. He says the process often requires a lengthy interview, access to a person's criminal and mental health history, and even special testing.
ROSENFELD: So when I'm asked to predict or to assess someone's violent risk I have a tremendous amount of information at my disposal that the typical mental health professional on the fly simply doesn't have.
HAMILTON: Even highly trained professionals, with lots of information, aren't that accurate.
Alan Teo of the University of Michigan compared the ability of young psychiatrists and more experienced ones to assess the risk that patients at a large psychiatric hospital would become violent. Half of the patients assaulted staff during their stay, the other half didn't.
ALAN TEO: The less experienced psychiatry residents were actually not any better than flipping a coin. They were no better than chance in predicting a patients' risk for violence.
HAMILTON: Teo says the experienced doctors did better - but were still wrong about 30 percent of the time.
TEO: Three out of 10 cases being missed when we're talking about assaults on staff or assaults on other patients is clearly unacceptable.
HAMILTON: There are a couple of pretty reliable signs that a person with a mental illness is likely to act violently.
Steven Hoge, a forensic psychiatrist at Columbia University, says it's a red flag if a patient has committed acts of violence in the past or is currently threatening violence. But with other patients, Hoge says, risk assessment is mostly guesswork.
STEVEN HOGE: For anyone to make an accurate assessment in the absence of either a past offense or a current threat is virtually impossible.
HAMILTON: Hoge says patients who are violent or threatening violence are pretty uncommon, and that mental health professionals tend to report them even without a special law.
Hoge also says that most mental health practitioners support the intent of gun control laws, like the one in New York. They just think the emphasis on the mental illness is misguided.
HOGE: The biggest risk for gun violence is a gun - possession of a gun. And the mentally ill, there's no evidence that the mentally ill possess guns or commit gun violence with any greater rate than the normal population.
HAMILTON: Of course, on rare occasions a person with a mental illness does commit a horrific act of violence. But Hoge says the bottom line is you can't assume that a mental health professional could have seen it coming.
Jon Hamilton, NPR News.
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