再Measuring risk, June 22nd 2013 P76 危険の数値化(書評)
Risk is everywhere. From tabloid headlines insisting that coffee causes cancer to stern government warnings about alcohol and driving, the world is teeming with goblins. For each one there is a frighteningly precise measurement of just how likely it is to jump from the shadows and get you. ゛The Norm Chronicles゛, a new book from Michael Blastland, a journalist in love with statistics, and David Spiegelhalter, a statistician, aims to help data-probes find their way through this blizzard of risks. To make risk comprehensible, the book uses a device called the MicroMort. One MicroMort is a one-in-million chance of death, which is roughly the risk of dying from an accident such as a car crash on an ordinary day in Britain. That baseline allows for illuminating comparisons. Giving birth in Britain, for instance, exposes thd mother to about 120 MicroMorts, about the same risk as riding a motorbike from London to Edinburgh and back, or from 2 1/2 days of active service during the most dangerous period of the war in Afghanistan. Life has plainly become much safer in recent decades. This is true even on the battlefield：soldiers in Afghanistan faced around 47 MicroMorts a day, but the aircrews that bombed Germany in the secoed world war endured about 25,000 MicroMorts per mission. The authors also introduce a related and equally eye-catching way of expressing risk, called the MicroLife - the amount, on average, by which a given activity shortens or lengthens one's life. Puffing 15-24 cigarettes a day, on average, robs a smoker older than 35 of five hours of life each and every day. But 20 minutes of moderate exercise a day earns almost an hour back. Alcohol wears a Janus face：the first drink of the day adds about 30 minutes per day to one's life expectancy, but each subsequent one cuts it back by 15 minutes. Grim stuff, yet the authors do not hector their readers. At one point they quote Kingsley Amis's aphorism that ゛no pleasure is worth giving up for the sake of two more years in a geriatric home at Weston-super-Mare゛. To help illustrate the relationship between deed and danger, the book employs a cast of three imaginary characters：cautious Prudence, reckless Kelvin and the titular Norm, as in ゛normal゛, who steers a middle course between brashness and paranoia. Each chapter is dedicated to a category of risk - from sex to extreme sport - and opens with a short and often amusing vignette featuring Prudence, Kelvin or Norm. The characters serve as a counterweight to the numbers and statistics, and convey the point that calculating risk is only half of the problem. Appetites vary, and an acceptable risk for one person - allowing children to play unsupervised, for instance - might be unthinkable to another. Messrs Blastland and Spiegehalter wear their learning lightly. They never lapse into the smug tone that often accompanies books like these, in which people who fear flying are mocked for their irrationality (as flying is, statistically, far safer than driving or walking). Yet the book's purpose is serious. Helping people make sense of the barrage of confusing (and often misrepresented) statistics that riddle every day is a noble goal. Making the process enjoyable is a real achievement.
