Suppose a test can determine with 99 percent accuracy whether someone has a certain disease, which only affects one out of every 10,000 people in the population. If a given person’s test comes back positive, what are the approximate odds that the person has the disease?
Test your math skills or your instincts by giving your best answer above, before reading on for the correct answer.See Answer and Explanation
The false positive paradox is a type of base rate fallacy, where prior probability information, in this case the incidence of the disease in the population, is ignored. This is a real problem in the field of medicine, as surveys indicate that many patients and even physicians simply do not understand how to interpret information such as cancer screening statistics.