If these data lead to reliable diagnostic tests, researchers could use them as a measuring tool to design studies of suicide that mirror the Framingham Heart Study, which has guided how we treat and prevent cardiovascular disease: 65 years ago, researchers began tracking the habits of and compiling regular medical workups on 5,209 residents of Framingham, Mass. It wasn’t initially clear what the data they were collecting meant. But over decades, as some people developed heart disease and others didn’t, their earlier test results and behavior began to reveal how high blood pressure and cholesterol, smoking, obesity and lack of exercise had helped cause it, how those factors could be entered into a calculator to determine risk and what would drive that risk down; once these insights led to treatments, the rate of deaths from heart disease nationwide, which had been steadily increasing since the turn of the century, began a steep decline.

Cognitive tests, of course, are not as fail-safe as a blood test. Nock says it is possible for patients taking the I.A.T. or the Stroop to adjust the speed of their keystrokes if they wish to hide their thoughts. “But it’s much more difficult to change the way you report on the test than to change the way you report verbally to someone.” Nock said. “It’s really easy to say: ‘I don’t want to kill myself. I’m totally fine.’ ” Anyone can choose not to reveal what he’s really thinking about. It’s much harder, Nock said, to trick the tests.

But even if the tests could offer a suicide-risk score right now, clinicians and researchers still have questions about how they would use the number to treat patients. “One of the things I wonder is what do you do if somebody tests positive on one of these things and they deny that they’re suicidal,” says David A. Brent, who holds an endowed chair in suicide studies at the University of Pittsburgh School of Medicine. “Admittedly I’d rather have the information than not. But it’s an interesting thing, you know, to say, ‘Look, according to this you are thinking about suicide.’ And would you be able to keep somebody in the hospital because of that? Would you change your treatment? I’m just not really sure.”

Nock’s refusal to accept any wisdom that can’t be tested, including the seemingly logical notion that simply getting more suicidal people into treatment would solve the problem, has put him at odds with clinicians who believe their methods work and that questioning those could cost lives. In January, in partnership with Ronald Kessler, an epidemiologist at Harvard, he published a study showing that about one in eight American teenagers reported experiencing serious suicidal thoughts. Strikingly, more than half of them were getting therapy before or during the period when they became suicidal. Some clinicians e-mailed Nock to express anger that he would make such statistics public. Their position, he said, was that if you tell people treatment’s not effective, they’ll stop coming. “But I think there’s a balance here,” Nock said. “Yes, we want people to get treatment. But at the same time, we want to make sure the treatment they are getting is effective.” Marsha Linehan, a psychology professor at the University of Washington, has shown that intensive therapy designed to change patterns of thinking and behavior can reduce the risk of attempted suicide among highly impulsive patients with severe emotional problems. This was the treatment Melissa received at McLean. Preliminary evidence suggests that other existing interventions might work too, but — largely because of how difficult it is to tell who is suicidal and when — a majority of people at high risk aren’t getting them.

A major investment of money and manpower from the Army is set to revolutionize the scope of collecting data on suicidal behavior. Nock and his team are participating in the Army Study to Assess Risk and Resilience in Servicemembers, which got under way in 2009 and is the most comprehensive investigation of suicide ever undertaken. The Army’s access to thousands of volunteers who lead comparable lifestyles and excel at following instructions offers a unique laboratory for Framingham-scale longitudinal studies. Nock envisions, for instance, one day beaming the I.A.T., Stroop and other tests to servicemembers’ phones daily — a technological feat unthinkable a decade ago. Those scores might reveal suicidal thoughts in real time. They might also offer a way to monitor patients known to be at high risk and call them if they seem to be entering a dangerous frame of mind.

“Right now, we ask people if they’re suicidal,” Nock said. “And if they say yes, we give them medication to try and make them less depressed or less anxious or less psychotic or to have a more stable mood. And then we talk to them. We do talk therapy. And essentially talk them into not being suicidal anymore. And this over all as a strategy for many people does not seem to be curative.” But if doctors could see which patients are suicidal at a given moment, they might be able to retrain their self-destructive thinking based on their test scores. If, as the I.A.T. seems to suggest, associating yourself more with dying than with living increases your risk for suicide, breaking that association might decrease it. To find out, Nock is developing computer tasks that he hopes could help get people, through rote practice, to identify more with being alive than dead. His researchers are also starting to test whether training people to think more positively about the past and the future makes them less likely to attempt suicide. Nock often talks about “turning levers,” as if he were a railroad-switch operator manning an existential junction. “Can we think of suicide as resulting from problems with memory or cognition or attention?” he said. “And if so, can we then turn levers on those things to make people less likely to think about suicide? So, it’s not giving a pill; it’s giving a training.”

Before I met Nock, I wondered what someone whose research requires constantly delving into the grief of others must be like. I imagined he would be solemn and weary. But he is a mechanic by background and temperament. His search for solutions is Socratic, not quixotic. He is an optimist. “It’s a complex problem,” he told me once, in his reasonable fashion, “but there are answers to it.” At this point in his career, he has asked hundreds of people why they tried to kill themselves. More often than not, their responses have fueled rather than dulled his curiosity.