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Calculated Risks: How to Know When Numbers Deceive You Paperback – March 19, 2003

ISBN-13: 978-0743254236 ISBN-10: 0743254236 Edition: 1st

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Product Details

  • Paperback: 320 pages
  • Publisher: Simon & Schuster; 1 edition (March 19, 2003)
  • Language: English
  • ISBN-10: 0743254236
  • ISBN-13: 978-0743254236
  • Product Dimensions: 6.1 x 1.1 x 9.2 inches
  • Shipping Weight: 1 pounds (View shipping rates and policies)
  • Average Customer Review: 4.6 out of 5 stars  See all reviews (29 customer reviews)
  • Amazon Best Sellers Rank: #107,910 in Books (See Top 100 in Books)

Editorial Reviews

Amazon.com Review

In the tradition of Innumeracy by John Allen Paulos, German scientist Gerd Gigerenzer offers his own take on numerical illiteracy. "In Western countries, most children learn to read and write, but even in adulthood, many people do not know how to think with numbers," he writes. "I focus on the most important form of innumeracy in everyday life, statistical innumeracy--that is, the inability to reason about uncertainties and risk." The author wisely uses concrete examples from the real world to make his points, and he shows the devastating impact of this problem. In one example, he describes a surgeon who advised many of his patients to accept prophylactic mastectomies in order to dodge breast cancer. In a two-year period, this doctor convinced 90 "high-risk" women without cancer to sacrifice their breasts "in a heroic exchange for the certainty of saving their lives and protecting their loved ones from suffering and loss." But Gigerenzer shows that the vast majority of these women (84 of them, to be exact) would not have developed breast cancer at all. If the doctor or his patients had a better understanding of probabilities, they might have chosen a different course. Fans of Innumeracy will enjoy Calculated Risks, as will anyone who appreciates a good puzzle over numbers. --John Miller --This text refers to an out of print or unavailable edition of this title.

From Publishers Weekly

If a woman aged 40 to 50 has breast cancer, nine times out of 10 it will show up on a mammogram. On the other hand, nine out of 10 suspicious mammograms turn out not to be cancer. Confused? So are many people who seek certainty through numbers, says Gigerenzer, a statistician and behavioral scientist. His book is a successful attempt to help innumerates (those who don't understand statistics), offering case studies of people who desperately need to understand statistics, including those working in AIDS counseling, DNA fingerprinting and domestic violence cases. Gigerenzer deftly intersperses math lessons explaining concepts like frequency and risk in layperson's terms with real-life stories involving doctors and detectives. One of his main themes is that even well-meaning, statistically astute professionals may be unable to communicate concepts such as statistical risk to innumerates. (He tells the true story of a psychiatrist who prescribes Prozac to a patient and warns him about potential side effects, saying, You have a 30 to 50 percent chance of developing a sexual problem. The patient worries that in anywhere from 30% to 50% of all his sexual encounters, he is going to have performance problems. But what the doctor really meant is that for every 10 people who take Prozac, three to five may experience sexual side effects, and many have no sexual side effects at all.) All innumerates buyers, sellers, students, professors, doctors, patients, lawyers and their clients, politicians, voters, writers and readers have something to learn from Gigerenzer's quirky yet understandable book.
Copyright 2002 Cahners Business Information, Inc. --This text refers to an out of print or unavailable edition of this title.

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Customer Reviews

This is a very clearly written book.
Gaetan Lion
It shows how to effectively reason about probabilities and risks and how to communicate them in a way that people can understand them.
Amazon Customer
Good book for students to read before taking any stats/ intro to stats class.

Most Helpful Customer Reviews

38 of 38 people found the following review helpful By Gaetan Lion on June 2, 2004
Format: Hardcover Verified Purchase
This is a very clearly written book. It demonstrates many numerical errors the press, the public, and experts make in interpreting the accuracy of medical screening test (mammography, HIV test, etc...) and figuring out the probability of an accused person being guilty.
At the foundation of the above confusions lies the interpretation of Baye's rule. Taking one example on page 45 regarding breast cancer. Breast cancer affects 0.8% of women over 40. Mammography correctly interprets 90% of the positive tests (when women do have breast cancer) and 93% of the negative ones (when they don't have breast cancer). If you ask a doctor how accurate this test is if you get a positive test, the majority will tell you the test is 90% accurate or more. That is wrong. The author recommends using natural frequencies (instead of conditional probabilities) to accurately interpret Baye's rule. Thus, 8 out of every 1,000 women have breast cancer. Of these 8 women, 7 will have a positive mammogram (true positives). Of, the remaining 992 women who don't have breast cancer, 70 will have a positive mammogram (false positives). So, the accuracy of the test is 7/(7+70) = 10%. Wow, that is pretty different than the 90% that most doctors believe!
What to do? In the case of mammography, if you take a second test that turns positive, the accuracy would jump to 57% (not that much better than flipping a coin). It is only when taking a third test that also turns positive that you can be reasonably certain (93% accuracy) that you have breast cancer. So, what doctors should say is that a positive test really does not mean anything. And, it is only after the third consecutive positive test that you can be over 90% certain that you have breast cancer.
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20 of 20 people found the following review helpful By A Customer on July 10, 2002
Format: Hardcover
In a valiant effort to educate professionals and lay people alike, the author of this book clearly explains how to interpret risks and risk data (statistics) in a useful and understandable way. For example, anyone who is wondering about whether or not to undergo screening for breast cancer, prostate cancer, HIV, etc. should do themselves a great big favor and read this book. The author also discusses legal issues such as how evidence may presented in court in order to support a given side of a case just by presenting statistical data, e.g., fingerprints, DNA evidence, etc., in certain ways. In addition, the author discusses a variety of other matters from advertising gimmicks to TV game show strategies. Using the techniques given in this book, readers will be much less likely to be fooled. Clearly written in plain english and in an engaging style, this book should be required reading for everyone - from professionals who provide statistical (risk) information (they would learn how to be more clearly understood) to those receiving the information (they would learn to see through any smoke screens or awkward presentations and thus make better decisions).
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20 of 20 people found the following review helpful By J. Williamsen on May 28, 2003
Format: Hardcover Verified Purchase
Gerd Gigerenzer has written several books dealing with "bounded rationality"--how humans use their brains to understand the world around them, make decisions, and determine the risks associated with a given course of action. This book is easily his most accessible. It is clear and easy to read, with most(but not all)the examples drawn from the field of personal health.
Gigerenzer provides the simple mental tools that allow anyone to make sense of the statistics that bombard us daily in the media. It is exactly his point that one does not need to be a rocket scientist (or professional statistician) to understand the numbers used by professionals, from personal physicians to DNA experts, that affect our lives and livelihoods.
If I could recommend only one book to address "numerical illiteracy," this would be it. You will learn some essential skills in a clearly informative and entertaining way.
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11 of 12 people found the following review helpful By Dad Ditty on December 28, 2005
Format: Hardcover
The book "Calculated Risk: How to Know When Numbers Deceive You", by Gerd Gigerenzer, will increase your risk aptitude. The 4 1/2 star (Amazon.com) book does not discuss statistical innumeracy from the IT perspective, but discusses innumeracy mainly in contemporary medicine, the justice system, and life in general.

Gerd describes four aspects of innumeracy as follows:

01) Illusion of certainty:

For example: Fingerprint and DNA testing.

02) Ignorance of relevant risks:

For example: "It is more likely that a young American male

knows baseball statistics than that his chances of dying on

a motorcycle trip is about 15 times higher than his chances

of dying on a car trip of the same distance."

03) Miscommunication of risks:

For example: One can communicate the chances that a test

will actually detect a disease in various ways ... The most

frequent way is in the form of a conditional probability: If

a person has cancer, the probability the he/she will test

positive on a screening is 90 percent. Many physicians

confuse that statement with this one: If a person test

positive on a screening, the probability that he/she has

cancer is 90 percent.

04) Drawing incorrect inferences from statistics:

For example: "Consider a newspaper article in which it is

reported that men with high cholesterol have a 50 percent

higher risk of heart attack. The figure of 50 percent

sounds frighting, put what does it mean?
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