All games
Cognitive Biases Base Rate Neglect
The Positive Test
A test comes back positive for a rare condition. Your gut screams that you have it. Three times, you will set how worried you would be — then meet the real math.
1Read each scenario: how rare the condition is, and how accurate the test is.
2Set your estimate of the real chance you have it, from 0 to 100 percent.
3See the true Bayesian answer and the 1000-person breakdown behind it.
The concept· Kahneman & Tversky, 1973; Bayes, 1763
Base Rate Neglect
Base rate neglect is when, judging a probability, we fixate on the specific evidence in front of us — a positive test — and ignore the base rate: how common the thing is in the first place.
It causes panic over rare-disease screenings, biased hiring, and bad risk calls whenever a "positive signal" meets a rare event. The signal feels decisive, but on a rare event it is mostly noise.