1. Young, Robert C. MD

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On January 13, 2013, CBS News Online reported that eating 150 grams of processed meat daily (the equivalent of six strips of bacon) increases your risk of developing pancreatic cancer by 57 percent. This and many other odd and commonplace statistical risks are explored in this book, a delightful romp through the world of statistics and psychology of risk perception.

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ROBERT C. YOUNG, MD.... - Click to enlarge in new windowROBERT C. YOUNG, MD. REVIEWED BY ROBERT C. YOUNG, MD Chairman,

The authors, two Brits-Michael Blastland a journalist, and David Spiegelhalter, a Cambridge University expert in risk perception-use a lighthearted, humorous style for a serious exploration of statistical risk and our human responses to those risks.


To provide us with a way to compare different risks, the authors employ an ingenious little tool called a MicroMort (MM). Since roughly one in a million Brits die of accidents each year, this one in a million defines 1 MM-although life in the United States is actually riskier (1.6 MMs). Using this tool one can equate the risk of anesthesia (5 MMs) with 20 miles of motorcycle travel: climbing Mount Everest (43,000 MMs), one scuba dive (7 MMs)-you get the idea.


MicroMorts measure acute risks. For chronic risks like smoking or obesity, the authors use MicroLives (MLs). One ML is about 30 minutes of life, selected because the average adult has about one million half hours of life remaining. Smoking costs you about 10 MLs a day, obesity 3MLs a day, being male 4MLs a day. Since MMs are acute risks, they disappear after the event, but MLs accumulate.


The book includes several large charts at the end comparing many common and unusual risks measured in MMs and MLs.


The authors skillfully explore, in uncomplicated terms, many arcane and at times misleading statistics. Take the bacon example mentioned earlier: First, it is unlikely that anyone would actually eat that quantity every day of their lives. And even if they did, about 1.5 percent of Americans develop pancreatic cancer in their lifetime. That's 5 in 400, and the risk in bacon addicts rises to only 6 in 400. Relative risks behave like a magnifying glass: If we consider the entire at-risk population, 395 of the 400 people avoid pancreatic cancer. In those who gorged on bacon, 394 of 400 are still fine.


The authors examine a variety of intriguing statistics about the normal risks of life, and while we tend to focus on external risks, natural risks abound: Being a newborn is risky-6,100 MMs in the first year. Childbirth is 210 MMs, or the equivalent of an 800 mile trip on a motorcycle. We accept the natural risks better because we lack any meaningful control over them and because we so greatly value the outcome.


But Blastland and Spiegelhalter argue that most people are not statisticians and don't see risks in the same way. To probe the psychology of risk perception, the book utilizes three characters: Norm, who seeks risk balance; Prudence, who is risk averse; and Kelvin, who enjoys risk.


Statisticians see risk in terms of numbers, but people assess risk through stories, anecdotes, and personal experience. Throughout the text, these three folks are used to illustrate how different people respond to a similar level of risk.


Crime elicits different responses depending on the nature of the crime. The more gruesome the crime, the more vividly it is remembered-and as a result, more often overestimated in frequency. Reality is often different. Children are 20 times more likely to be injured by their parents than by strangers (0.4% of abductions) or by sex offenders (1.5% of abductions). Of the approximately 260,000 abductions that take place every year, 200,000 are by relatives.


Fear of flying is a dramatic example of a disconnect between perception and reality: Three to five percent of people won't fly, 17 percent are afraid, and 30 to 40 percent have moderate anxiety when flying. Yet in reality, commercial flying is extremely safe-measured in MicroMorts, the risk is 0.02MMs. The authors remind us that you would have to take 50 million flights before you are likely to have a fatality. One flight a day would take you 120,000 years. Comforting thought.


'Illusory Superiority,' 'Denominator Neglect'

But why do we have this misperception? First because it's a catastrophic event and understandably frightening, and second because it's completely beyond our control. We humans always have the belief that we can produce better outcomes if we are in control-what the authors call "illusory superiority."


One of the most provocative chapters in the book is entitled "Nothing," which examines the concept of "denominator neglect"-i.e., that it's easier for humans to imagine events than to conceptualize non-events. The media contributes to the difficulty. For example, you never see headlines proclaiming "No children killed on the way to school today," but rare, exotic events ("Mad Cow disease") are covered widely. Comparatively common events (smoking-related deaths) are seldom covered.


The authors finish the book by attempting to reconcile the two faces of risk: The orderly view of population risk seen in the numbers, contrasted with the jumbled human response based on widely varying personal perceptions of individual risk-benefit.


Blastland and Spiegelhalter conclude that "Norm, Prudence, and Kelvin are not irrational when they choose to ignore the numbers and go their own way. The measure of what people perceive as risk is a matter of personal value and personal framing."


Indeed, individual conclusions about risk are highly dependent on how the risk data are framed when presented. "Evidence-Based Risk Communication" was explored in a recent Annals of Internal Medicine article (2014;161:270-280). Those authors tested various ways of communicating risk, concluding that visual aids and absolute risk formats improve patient's understanding, whereas numbers needed to treat can lessen understanding. Presenting benefits before harms improved accuracy, but decreased acceptance of treatments.


The Norm Chronicles is a spirited and entertaining expedition through the complex world of risk perception. It is heavily weighted on British statistics but contains enough American data to secure its relevance to domestic readers.


The upbeat treatment of the contrasting aspects of risk makes the book valuable for oncologists and other medical folks as well as for the general public.




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