May 1st 2003ArticleLetter to the Editor
In the excellent online magazine The Edge (www.edge.org), Gerd Gigerenzer, director of the Center for Adaptive Behavior and Cognition at the Max Planck Institute for Human Development in Berlin, poses a riddle about risk: Imagine that a 40-year-old woman has her first mammogram and it comes back positive. The incidence of the disease in her age group is 1 percent. The test is 90 percent accurate, and it has a false-positive rate of 9 percent. What's the probability that the woman has cancer?