Schneier on Security

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April 13, 2010

Terrorist Attacks and Comparable Risks, Part 2

John Adams argues that our irrationality about comparative risks depends on the type of risk:

With "pure" voluntary risks, the risk itself, with its associated challenge and rush of adrenaline, is the reward. Most climbers on Mount Everest know that it is dangerous and willingly take the risk. With a voluntary, self-controlled, applied risk, such as driving, the reward is getting expeditiously from A to B. But the sense of control that drivers have over their fates appears to encourage a high level of tolerance of the risks involved.

Cycling from A to B (I write as a London cyclist) is done with a diminished sense of control over one's fate. This sense is supported by statistics that show that per kilometre travelled a cyclist is 14 times more likely to die than someone in a car. This is a good example of the importance of distinguishing between relative and absolute risk. Although 14 times greater, the absolute risk of cycling is still small -- 1 fatality in 25 million kilometres cycled; not even Lance Armstrong can begin to cover that distance in a lifetime of cycling. And numerous studies have demonstrated that the extra relative risk is more than offset by the health benefits of regular cycling; regular cyclists live longer.

While people may voluntarily board planes, buses and trains, the popular reaction to crashes in which passengers are passive victims, suggests that the public demand a higher standard of safety in circumstances in which people voluntarily hand over control of their safety to pilots, or to bus or train drivers.

Risks imposed by nature -- such as those endured by those living on the San Andreas Fault or the slopes of Mount Etna -- or impersonal economic forces -- such as the vicissitudes of the global economy -- are placed in the middle of the scale. Reactions vary widely. They are usually seen as motiveless and are responded to fatalistically - unless or until the threat appears imminent.

Imposed risks are less tolerated. Consider mobile phones. The risk associated with the handsets is either non-existent or very small. The risk associated with the base stations, measured by radiation dose, unless one is up the mast with an ear to the transmitter, is orders of magnitude less. Yet all round the world billions are queuing up to take the voluntary risk, and almost all the opposition is focussed on the base stations, which are seen by objectors as impositions. Because the radiation dose received from the handset increases with distance from the base station, to the extent that campaigns against the base stations are successful, they will increase the distance from the base station to the average handset, and thus the radiation dose. The base station risk, if it exist, might be labelled a benignly imposed risk; no one supposes that the phone company wishes to murder all those in the neighbourhood.

Less tolerated are risks whose imposers are perceived as motivated by profit or greed. In Europe, big biotech companies such as Monsanto are routinely denounced by environmentalist opponents for being more concerned with profits than the welfare of the environment or the consumers of its products.

Less tolerated still are malignly imposed risks -- crimes ranging from mugging to rape and murder. In most countries in the world the number of deaths on the road far exceeds the numbers of murders, but far more people are sent to jail for murder than for causing death by dangerous driving. In the United States in 2002 16,000 people were murdered -- a statistic that evoked far more popular concern than the 42,000 killed on the road -- but far less than the 25 killed by terrorists.

This isn't a new result, but it's vital to understand how people react to different risks.

Posted on April 13, 2010 at 1:18 PM • 12 Comments

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