Why A Mass Shooting Is Hard—Even Impossible—to Predict

Richard J. McNally, a licensed clinical psychologist and professor at Harvard University, insists that most people with mental illnesses are not violent.


“Police vehicles block entrance – Washington Navy Yard shooting” by Tim Evanson/Flickr

On Monday, a gunman opened fire inside the Washington Navy Yard, killing 12 people before authorities shot him to death. In the days following the mass shooting, reports surfaced indicating that the gunman, Aaron Alexis, showed signs of mental illness, such as auditory hallucinations and paranoia.

The Navy Yard shooting—the fifth mass shooting in the U.S. this year—once again brings mental health issues into the national spotlight, raising questions of whether we can predict such tragedies before they happen and the proper ways to prevent them.

Richard J. McNally is a licensed clinical psychologist and professor at Harvard University, where he leads the McNally Laboratory in research on anxiety and related disorders. He suggested in a 2011 Salon article following the shooting in Tucson, Arizona that no, psychiatrists cannot predict mass murderers.

In light of the Navy Yard shooting, Professor McNally reaffirmed his position and offered other takeaways:

1. Although mass shooters exhibit similar characteristics, most people with such characteristics are not prone to violence.

Aaron Alexis joins a list of mass shooters, including James Holmes and Adam Lanza, who showed signs of suffering from mental illness before committing murder. But just because they share a set of characteristics doesn’t mean that these characteristics can be used to predict the next incident, according to McNally.

Alexis, for example, appears to have suffered from schizophrenia, an illness that affects about 1.1 percent of Americans 18 or older, according to the National Institute of Mental Health. He reported command auditory hallucinations, which according to McNally, occur in about 30 percent of schizophrenia cases and are mostly benign—commands to open the window or get a coffee, for example—rather than violent.

“The [characteristics] are all so relatively common, but mass murder is extremely rare,” said McNally. “When you have a bunch of predictors that are correlated with mass murder and you’re trying to predict the occurrence of mass murder based on, let’s say, paranoid schizophrenia diagnosis, including command hallucinations, most of the predictions will turn out to be false positives.”

At the very core, it’s a statistical problem.

“I think people who are conversant with the research literature and also understand the statistics of prediction would agree with me. When predictors are common and the predicted event is rare, the danger of over-predicting is very great,” he said.

2. The shock factor of mass shootings distorts our way of thinking, leading us to believe that they could’ve been predicted.

Following a shocking event, humans tend to show “hindsight bias,” falling under an illusion that the event was inevitable, predictable, and preventable, according to McNally.

“But that’s not the situation we have at the outset, where we have lots of people with these characteristics and only a tiny fraction of them will actually go on to commit a horrific atrocity like this,” he said.

In fact, people with mental illnesses are more likely to be victims rather than perpetrators of violence, according to McNally.

“It’s good to keep that in mind because when you get a case with someone with a mental illness who commits a terrible crime, the salience—the shocking, emotional salience—of this tends to distort our understanding of how things are,” he said. “Really shocking, distorting events—we tend to perceive them as more probable or common or likely than they actually are. Again, this is just how the mind works when it comes to computing probabilities.”

3. Mental health treatment and gun control are both important.

The two can go hand in hand. Seemingly simple measures—such as putting up barriers on a single bridge—can decrease suicide rates. The same method can be applied to preventing mass shootings by increasing gun control measures, according to McNally.

“People who are suicidal get fixated on dying in a certain fashion and if something prevents them even temporarily, the crisis often subsides,” he said. “Sometimes simple preventive interventions across the board can delay a person in committing suicide or homicide and in virtue of that, the person gets help and no one dies.”

But mental health treatment can’t be imposed—and therein lies another issue.

“Involuntary treatment only comes in if they’re an imminent danger to themselves or to others,” said McNally. “It’s a delicate balance here—protecting the civil rights of individuals and protecting the safety of other people in society.”

4. Despite criticism that media coverage can serve as motivation for other mass shooters, the media can better inform the public on mental health issues. That’s helpful as people suffering from mental illness don’t always recognize it themselves.

Publicity is an inevitable outcome, but most of the time not a central motivation to commit crime, according to McNally.

“This is the fastest, surest way of being on everybody’s mind, having your name on the lips of every person in the United States—to commit one of these outrageous crimes,” he said. “But there’s other motivations, not just publicity that’s driving this. It’s easy to get your name in a newspaper by doing something outrageous, but committing mass murder is not the first thing that would come to people’s minds.”

McNally recognizes the media’s job to report the news, but encourages the spread of more information about mental health treatment.

“Sometimes [people with mental illnesses] lack insight into their own problems when they’re in the grips of psychosis. It’s a loss of contact with reality, including the reality to be able to understand the source of their suffering,” he said. “Usually what happens is if the person has connections with family or friends or colleagues, they can notice these things and urge the person to get help. That’s one role the media can play—educating the public.”

5. Mass shootings can reinforce a stigma against people with mental illnesses and it’s important to prevent that from happening.

“We have to be mindful of the fact that the vast majority of people who show these characteristics are not prone to violence, let alone violence in this dramatic fashion. One concern is that people start taking these cases and assuming they’re typical of people with schizophrenia—they’re not,” said McNally. “Educating the public about statistical facts can help calm that stigma.”