JUST WHAT ARE OUR RISKS?

Crunching the Risk Numbers

Most of us are horrible assessors of risk. Travelers at American airports are taking extensive steps due to fears of terrorism. But in the decade of the 2000s, only about one passenger for every 25 million was killed in a terrorist attack aboard an American commercial airliner (all of the fatalities were on 9/11). By contrast, a person has about a one in 500,000 chance each year of being struck by lightning.
The usual response I get to these statistics—especially in the wake of Umar Farouk Abdulmutallab's attempt to bring down Northwest Flight 253 on Christmas Day—is that although terrorist incidents aboard airplanes might never have been common, they are becoming more so. This belief, too, is mistaken. Relative to the number of commercial departures world-wide, passenger deaths resulting from what I term "violent passenger incidents"—bombings, hijackings, and other sabotage—were at least five times less common in the 2000s than in any decade from the 1940s through the 1980s.
Indeed, 9/11 looks like a horrible outlier. While it killed nearly 3,000 citizens, no other individual terrorist attack in the modern history of the 38 most highly developed nations has killed more than 329. Meanwhile, a literal repeat of 9/11 is unlikely, as Al Qaeda's diabolical innovation—turning a passenger jet into a missile—would almost certainly be thwarted by brave passengers (and secure cockpit doors).
Overall, academic and governmental databases report, terrorist attacks killed a total of about 5,300 people in the most highly developed nations since the end of the Cold War in 1991, a rate of about 300 per year. The chance of a Westerner being killed by a terrorist is exceedingly low: about a one in three million each year, or the same chance an American will be killed by a tornado. (The Department of Homeland Security's budget is 50 times larger than that of the weather service).
Nor is it clear that the threat from terrorism is increasing. The years between 2005 and 2009 (313 fatalities), in fact, represents the second safest period on record since at least 1970.Surely some of this is because of improved vigilance and intelligence. As well, other once-threatening terrorist organizations—like the Irish Republican Army, Islamic Jihad, the PFLP, and the Libyan extremists who brought down the flight over Lockerbie, Scotland,—have become dormant or de-radicalized.
There is one concern that rates as a clear exception to these statistics: the threat of terrorism involving nuclear weapons. The renowned Harvard scholar Graham Allison has posited that there is greater than a 50% likelihood of a nuclear terrorist attack in the next decade, which he says could kill upward of 500,000 people. If we accept Mr. Allison's estimates—a 5% chance per year of a 500,000-fatality event in a Western country (25,000 causalities per year)—the risk from such incidents is some 150 times greater than that from conventional terrorist attacks. Other scholars consider the chance of a nuclear incident to be much lower. Even if Mr. Allison has overestimated the risk by fivefold, and the number of causalities by threefold, it would still represent 10 times the threat that conventional terrorism does.
In other words, a more rational anti-terrorism policy would focus resources heavily, perhaps almost exclusively, on threats of nuclear and weapons of mass destruction terror. The good news is that, because it requires so much coordination to acquire fissile material, build a nuclear weapon, and successfully detonate it, the international community has many opportunities to stop such catastrophes before they occur—although Mr. Allison and other experts contend that present efforts are inadequate.
Other sorts of terrorist attacks are not so easily deterred. There's really nothing preventing someone from committing a suicide attack at a shopping mall, or a movie theater, or a sporting event. This is not to suggest that no efforts should be made to stop them. But surely we must understand that, at best, we will reduce the risk from an extremely small nonzero number to a slightly smaller nonzero number. And we must be aware of the potential trade-offs. For instance, although it might be politically incorrect to talk about the hardship imposed by adding 15 minutes to each passenger's journey because of increased screening at the airport, if that time is worth $20 per hour this would be taking about $3.5 billion of productivity out of the economy each year. (The FAA considers a measure to be "cost-effective" it if saves one life per $3 million spent, so such screenings would have to prevent 1,150 fatalities per year to meet its benchmark.)
This is not to suggest that no efforts should be made to stop "conventional" terror attacks. But surely we must understand that, at best, we will reduce the risk from an extremely small nonzero number to a slightly smaller nonzero number.
Many object to this sort of analysis—no cost is too high, they say, to prevent the next 9/11. But if history is any guide, the next attack will probably not be like 9/11—it will be like NWA 253, something which threatens the lives of dozens or hundreds of people, not thousands. To the extent we overreact to these incidents—allowing them to disrupt our economy and our way of life—we do little but increase the value to terrorists of committing them.