Book Brief: Calculated Risks: How to Know When Numbers Deceive You

By Gerd Gigerenzer

Simon & Schuster Inc., June 2002

320 pages, $25

It is no longer news that many people don't understand numbers. Weathermen really do say "there is a 50 percent of rain on Saturday and a 50 percent chance of rain on Sunday, so it is guaranteed to rain this weekend." So the real contribution that Gigerenzer, a German scientist, makes here is how to deal with the problem, whether you are interacting with the people who report to you or with top management. His message: Forget percentages and "regressions to the mean," and put the numbers in simple language that even a CEO can understand.