An enviably close and influential collaboration during the 1970s between the psychologists Amos Tversky and Daniel Kahneman reshaped our beliefs about intuitive probabilistic reasoning. One of their many contributions was a demonstration of the base-rate fallacy, the tendency for people to neglect prior probabilities, or “base rates,” when calculating the chances of an event given more specific data.1 For example, the chances that a patient has a disease being tested reflects not only the test result and the test’s sensitivity and specificity, but also the relevant base rate, which is the prevalence of disease in a specific population.