Base-rate neglect
Definition · Level 11 · Interview practice
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Ignoring how rare a condition is when reading a test result. Fix it with Bayes via natural frequencies: count true and false positives in 10,000 people.
Example
1% prevalence, 99% sensitivity, 5% false positives → P(sick | +) = 99/594 ≈ 16.7%.
Where Tradecraft teaches it
Level 11 · Interview practice, in the lesson “Probability & expected value classics”: The puzzles interviewers often recycle, and the five tools that crack them.
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