AILSA CHANG, HOST:

Lawmakers are trying to decide what they can do now to prevent future mass shootings from happening. And one phrase that keeps coming up again and again is mental health.

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LINDSEY GRAHAM: What I want to look at is the mental health science.

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PAUL RYAN: Do we have the kind of mental health laws that we need on the books?

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JOHN CORNYN: ...Whether mental health officials could have done more.

CHANG: That's all from this week, all from Republican lawmakers - Senator Lindsey Graham of South Carolina, House Speaker Paul Ryan and Senator John Cornyn of Texas. We're now going to turn to Jonathan Metzl. He is a psychiatrist and professor at Vanderbilt University. Welcome.

JONATHAN METZL: Thanks so much for having me.

CHANG: First of all, I know that you take issue with this call from politicians that mental health professionals like you need to step up and help prevent gun violence. Why do you think that's the wrong way to approach this?

METZL: Well, certainly we should all do everything we can to prevent gun violence, and I think that mental health expertise is an important part of the conversation. But the reason that I and other people in my position write against this is first of all because people with mental illness are not a particularly high-risk group for gun violence or for mass shootings.

There's no psychiatric diagnosis that's aligned with harming other people, let alone shooting people. And the diagnoses that get thrown around in the aftermath of these horrible crimes like schizophrenia or depression, other factors like that, themselves are not aligned with violent attacks toward other people. And in that regard, there also are no tools that psychiatrists can use to say this one person with mental illness is going to harm somebody else, and this other person is not.

And I guess the last reason is that, as we're seeing after the horrible mass shooting in Florida, many mass shooters don't meet the criteria for severe mental illness in any way that would cause them to be flagged on a background check system, let alone hospitalized in a psychiatric hospital.

CHANG: How much interaction is there between mental health professionals like you and the background check system?

METZL: Well, the only way that someone can get their name on the federal background check system from the perspective of mental illness is either to be involuntarily committed to a mental hospital or if a court or government body declares a person mentally incompetent. And this is a very small sliver of patients who psychiatrists see.

First of all, the bar for admitting someone to a psychiatric hospital is quite high and particularly if that person is being admitted against their wishes. And even then, most people are released within a 72-hour period so don't meet the criteria for the background check system where a judge decides that they have to stay in for a longer period of time.

And even after that, if their name is entered into a background check system, people can buy guns at gun shows - there are many different loopholes - or just borrow guns from family members. And so in this sense, it's a very inexact science and unfortunately not a very effective one at this point.

CHANG: After a mass shooting happens, it's easy to conclude that the person who committed mass murder is a mentally troubled person. But there are all these social and environmental factors going on in that person's life. Not everything rises to the level of a diagnosable, treatable disease. So it places you in this precarious position where you have to be predictive when it's a mushy assessment.

METZL: It's a very mushy assessment. That's - I think that's really the key take-home point - is that psychiatric diagnosis is itself not a predictive science. In other words, there's nothing in psychiatric diagnosis that's going to tell you how somebody is going to act in one week or one year. And in that sense, putting psychiatrists in the position of having to predict something in the future is really at odds with their expertise.

CHANG: So if it is so difficult to be predictive, how do mental health professionals get involved in this conversation about curbing gun violence?

METZL: Psychiatrists are really good at looking at broader societal factors that look at prevention - in other words, what kinds of people or communities are at high risk across the board. For example, we know that if there is an interpersonal altercation and people are inebriated, there's alcohol present and there's a gun lying nearby, that that altercation is more likely to end in some kind of shooting. And so why is it that we have policies that allow people to carry loaded handguns into bars in many states?

We also know that gun violence happens within social networks. For instance, you're much more likely to be shot by your neighbor, your cousin, your boyfriend, your partner than you are by some random stranger. And so we should also track gun violence within social networks. These are all societal factors that are not linked directly to mental illness diagnosis.

CHANG: So what it sounds like is the legislative options about mental health are limited.

METZL: I think they don't pay attention to trends that we know happen in gun violence in the society. This is not to say that mental health expertise isn't an important part of the conversation, but it's just one piece of the broader conversation about what our society should do to, on one hand, respect people's rights and, on the other hand, create safer society.

CHANG: All right, that's Jonathan Metzl. He's a psychiatrist who directs the Vanderbilt University Center for Medicine, Health and Society. Thank you very much.

METZL: Thanks so much. Transcript provided by NPR, Copyright NPR.