By Shankar Vedantam
Monday, September 24, 2007
Shortly after the Sept. 11, 2001, attacks, psychologist Jennifer Lerner conducted a national field experiment: She asked a random sampling of Americans how likely it was that they would be the victim of a terrorist attack in the next 12 months.
Respondents said there was a 1-in-5 chance they would personally be hurt within the next year, and a nearly 1-in-2 chance that the average American would be hurt. That kind of carnage, Lerner estimated, would not have occurred even if there had been a Sept.11-scale attack every day of the year.
The purpose of Lerner's experiment was not to mock people's fears -- in the aftermath of the attacks, no one knew what to expect. If 19 hijackers armed with nothing more than box cutters could demolish the World Trade Center, damage the Pentagon, crash four airliners and kill nearly 3,000 people, who knew what else was coming?
What the experiment did highlight, however, was the role of psychological processes in biasing people's judgment when it comes to assessing risk. The study by Lerner, who is now at the Center for Public Leadership at Harvard's Kennedy School of Government, and other research show that when people are asked to make judgments about risk in uncertain situations, they fall back on mental rules of thumb that regularly turn out to be preposterously wrong.
Lerner found that anger and fear systematically bias people's risk estimates in opposite directions. Anger causes people to underestimate risks, which may be why drivers in the grip of road rage confidently attempt perilous maneuvers that place themselves and others in danger. By contrast, people who are afraid overestimate risks.
Research going back three decades shows that people are more likely to worry about unusual risks and less likely to worry about everyday dangers. Carnegie Mellon psychologist Baruch Fischhoff once found that people overestimate the number of deaths caused by accidents, tornadoes, floods, cancer, fires and homicides, and underestimate the risks of diabetes, stroke, asthma and emphysema.
To put it another way, people worry a lot more than they should about the kind of scenarios depicted in Hollywood thrillers and the nightly news, and worry a lot less than they should about "mundane" risks that do not make for gripping entertainment but kill a lot more Americans every year.
Malevolence or negligence on the part of others also seems to trigger our warning systems much more easily than the risks we pose to ourselves by smoking or leading sedentary lives. The number of Americans who have committed suicide in the past six years is more than 50 times the number of Americans killed by al-Qaeda operatives on Sept 11, 2001.
"The risk for any given person for suicide, particularly for middle-aged older white males, is dramatically higher than the risk of being mugged or being in a terrorist attack," Lerner said.
While psychology is not much use in predicting the future when it comes to terrorism, what it can do is highlight errors in thinking. Psychologist David Mandel asked people after the Sept. 11 attacks what they thought the risk of a major terrorist attack would be in the next two months. He then asked his volunteers to estimate the risk of an attack specifically by al-Qaeda and the risk of an attack by a completely separate group. Mandel found that when he totaled a person's responses about the likelihood of each of the subdivided possibilities, their sum was greater than the person's guess about the overall likelihood of a terrorist attack.
"By splitting the event into a terrorist attack by al-Qaeda or non-al-Qaeda operatives, that inflates the estimate the event will happen," said Mandel, who works for Defense Research and Development Canada, a government agency.
Subdividing a risk -- worrying not just about terrorism, in other words, but about nuclear terrorism and biological terrorism and hijacked planes and so on -- inflates the overall risk of terrorism in our minds. Mandel's point is not that subdividing risks leads to bad judgments, but rather that asking ourselves the same question in different ways often produces different answers. Mandel's insight is that it is not easy to know whether people's estimates of risk are accurate, since judgments about terrorism involve uncertainty, but that it is possible to discover whether their predictions of risk are coherent. A lack of coherence is one sign that accuracy might be in doubt as well.
Mandel has also found that when he asks people about the odds of a terrorist attack happening and the odds of an attack not happening, their answers regularly fail to add up to 100 percent. And Lerner's field experiment confirmed another puzzling thing: People invariably see themselves as being at lower risk than the average person -- they guessed that they had a 1-in-5 chance of being hurt but that others had a 1-in-2 chance of being hurt. Obviously, these statistics cannot be true for everyone.
"Not only is human judgment biased, but the problem is we are often unaware of the biases that affect our judgment," Mandel said. "When we are told people are biased in a particular manner, we think, 'Perhaps they are, but not me.' "