Bayes' Theorem
Also called: Bayes rule, Bayes theorem, Bayes law
Bayes' theorem tells you how to update a probability when new evidence arrives, combining prior belief with the likelihood of what you observed. Its most useful lesson is about base rates: a 99% accurate test for a condition affecting 1 in 10,000 people still produces mostly false positives, because the rare truth is swamped by the common error. Ignoring that is the base rate fallacy.
Formula
P(A|B) = P(B|A) × P(A) ÷ P(B)
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