Calculated Risks: How to Know When Numbers Deceive You

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