Dr. Gerd Gigerenzer with the Max Planck Institute for Human Development in Berlin recently asked 1,000 gynecologists what the chances a women with a positive mammogram actually has breast cancer. He provided the doctors with the statistics they needed for the women in their region: 1% prevalence of breast cancer (the probability a woman has cancer); 90% sensitivity of breast mammography (the probability a woman with breast cancer will test positive) and a 9% false-positive rate (the probability that a women without breast cancer will test positive).
Only 16% of the doctors could give the correct answer. Most doctors “grossly overestimated the probability of cancer, answering 90% or 81%,” Dr. Gigerenzer said. In fact, the number of doctors who got the answer right was slightly less than chance (21%)!
The correct answer: “Only one out of ten women with a positive mammogram will actually have breast cancer.”
