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What We Talk About When We Talk About Danger

The Norm Chronicles: Stories and Numbers About Danger and Death, Basic Books, 2014, 384 pp, $10.94.

Which is more dangerous, drinking a cup of coffee or eating a hamburger? According to the new book The Norm Chronicles: Stories and Numbers About Danger and Death, the hamburger is definitely the dicier option, and will, on average, shave a half hour off your life expectancy. Drinking two to three cups of coffee in one day, on the other hand, will add an extra 30 minutes to your life, statistically speaking. The Norm Chronicles is a guide for the layperson to something that actuaries deal with every day: risk. The authors have compiled a comprehensive guide to the hazards we encounter in our daily lives, including choosing between a trip to McDonalds and a stop at Starbucks. But they also look behind the data to illuminate the psychological aspects of weighing risks, shining a light on all the things, other than probability, that influence people’s choices.

Fittingly enough for a book that combines numbers and stories, The Norm Chronicles is the work of a mathematician, David Spiegelhalter, and a journalist, Michael Blastland. Spiegelhalter is officially known as the Winton Professor of the Public Understanding of Risk at Cambridge University. Blastland is a British journalist who has spent much of his career writing about numbers, and the co-author of The Tiger That Isn’t, a guide to understanding statistics. In order to capture both the numbers and the stories in the book, the authors began by compiling a great deal of data on dangers, both well known and obscure. In the chapter on health and safety at work, for example, they note that 14 people were killed in the London beer flood of 1814 when giant vats of porter burst at a brewery, and that a similar disaster in Boston involving an enormous tank of molasses claimed 21 lives in 1919. Spiegelhalter and Blastland then weave that data into the life stories of three characters: the perfectly average Norm, the perpetually cautious Prudence, and the reckless Kelvin and his brothers. They follow this trio through their lives, from growing up to their eventual demise, covering accidents, gambling, extreme sports, surgery, and dangers posed by outer space objects along the way. The approach allows the authors to show how a person who takes probability very seriously, a cautious person and a thrill-seeker might approach the same decision.

Although it’s written for a general audience, this survey of life’s dangers highlights a problem area for actuaries. The authors contend that communicating with people about risk is complicated by a host of factors that go far beyond the data. According to Michael Blastland, “There are 101 different things that make a difference to the answer to the question, ‘how dangerous is that?’ These can include errors people make in probability, but also their values, perceptions of risk, and [psychological] baggage.” Deciding whether to drive or to fly is a classic example of psychological factors at work. “You may decide to drive rather than fly,” says David Spiegelhalter, “because you think that if you get into a car accident, at least it was your own fault.” Relying on a pilot robs many people of that reassuring feeling of being in control. In other words, even though flying is much safer than driving, many people just feel safer in a car. (Nervous flyers may wish to avoid the chart in the book’s transportation chapter). This gap between data and behavior highlights a major problem in talking about risk. As Blastland points out, “If somebody simply says, ‘don’t jump off mountains wearing a wing suit, that’s dangerous,’ there’s a ready answer to that: ‘But I like it, I enjoy it, it’s part of who I am.’ That’s not stupid, that’s just a simple kind of statement about what it means to be a normal, rounded human being.”

The authors also believe that stories about risk convey more than numbers alone. “I’ve realized that just bombarding people with numbers is not a very effective way of communicating,” says mathematician Spiegelhalter. “Wrapping things up in narratives and stories is a much more powerful method to get through to people … It’s how we understand things as human beings; we turn everything into stories.” The vivid power of a good anecdote carries a dark side as well, he says. “Somebody who can tell a good story, but actually ignores the evidence, is quite a dangerous animal.”

In order to bring the evidence of risk to life, Spiegelhalter and Blastland rely on two innovative measurements, the micromort and the microlife. The micromort, which was pioneered by Stanford University professor and decision analyst Ronald A. Howard, represents a one in a million probability of dying. As it turns out, an American’s risk of dying suddenly and violently from external causes equals 1.3 micromorts per day. Spiegelhalter describes this daily 1.3 micromorts as “an inevitable baseline of risk, just because the asteroid might come through the roof at any time.” But he didn’t think the micromort was a good way to measure all of life’s risks. “The micromort is a unit of sudden death,” he says, while “things which harm you in a chronic way … the smoking, the drinking, the bad diet … are much more difficult to deal with. So we invented a new unit.” Speigelhalter came up with the idea of the microlife, a span of life 30 minutes long, which is “based on the idea that as young adults, we typically have about 1 million half-hours left to live, on average.”

The two measures allow for apples-to-apples comparisons. For example, in the U.S., the probability of suddenly dying while driving 240 miles equals one micromort, as does the probability of suddenly dying while riding a motorcycle for four miles or traveling 6,300 miles by train. For men and women over 35, eating the recommended five servings of fruits and vegetables adds four microlives to one’s lifespan every day, compared to the two microlives gained for the first 20 minutes spent exercising.

After putting all the data and stories together, journalist Blastland has some advice for presenting ideas about risk. For starters, remember the psychological factors that people bring to the discussion. “As soon as you accept that risk is not simply a matter of defining an objective probability, then you have to say, what else is it about?” he says. “And one of the things that it’s about is people’s sense of value in life, what matters to them, and also their sense of identity.” The debate over global warming may be a good example of this phenomenon. Blastland credits Dan Kahan of Yale University, who studies how cultural factors shape people’s opinions of risk, for influencing his own approach. For example, Blastland points out that in the case of climate change, people who highly value personal freedom can feel threatened by calls to restrict those freedoms, such as by mandating what kind of cars are allowed on the road. “I would think hard about how to represent this problem in a way that does not threaten people’s cultural identity,” Blastland says, suggesting that more emphasis on technological solutions, rather than fixes which involve restrictions, might be a better tactic to use when speaking with those who put a premium on individual rights. “Some part of people’s attitude toward risk is to do with their cultural identity, so let’s be aware of those cultural identities when we argue.”

The authors show how a person who takes probability very seriously, a cautious person and a thrill-seeker might approach the same decision.


By the time they finished the book, both authors were surprised by what they had learned. “One of the things I was amazed by is how safe things have become,” says Spiegelhalter. “When I was young, a thousand kids a year were killed in Britain on roads. And that’s gone down by 95%.” Blastland concurs, noting that “by age 10 in the U.S., you are the safest age you’ve ever been, and you ever will be, in the whole history of humanity.” But paradoxically, being safer doesn’t translate into feeling safer. “I suspect I was more anxious for my children than my parents were for us,” Blastland says. “You can say, I think these parents are just fools, or the numbers don’t tell you the whole story. And if they don’t, okay, well now it’s getting interesting.”

David Spiegelhalter says he’d like people to realize “that there are bits of Norm, Prudence and Kelvin in all of us. I would like there to be a bit more Norm.” But in the end, Blastland says, “We didn’t want to preach to anybody.” Instead, the two authors developed a statement they return to time and again: “Let’s compile the data as well as we can, and then invite people to do what they damn well please.”

“It’s no business of ours, really, what kind of choices people make,” says Michael Blastland, “but we hope we could at least give them this data as accurately as possible.”

Laurie McClellan is a freelance writer living in Arlington, Virginia.