In many ways, Bayes’s rule is a distillation of the scientific method. The textbook description of the scientific method goes something like this: (1) formulate a hypothesis, (2) deduce a testable consequence of the hypothesis, (3) perform an experiment and collect evidence, and (4) update your belief in the hypothesis. Usually the textbooks deal with simple yes-or-no tests and updates; the evidence either confirms or refutes the hypothesis. But life and science are never so simple! All evidence comes with a certain amount of uncertainty. Bayes’s rule tells us how to perform step (4) in the
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