Five pieces of 25% evidence add up to 76%? Lawyer's probability take sparks Bayesian correction

dilanesper · x · 2026-09-20

Lawyer @dilanesper argued people struggle to combine evidence: five pieces each making a defendant "25% likely guilty" supposedly add up to 76% probability.

AI researcher Quintin Pope quickly pushed back: probabilities can't be multiplied that way, and "25% likely guilty" says nothing about the strength or direction of evidence — moving from a 0.01% base rate to 25% is strong evidence of guilt, while dropping from 99% to 25% is evidence of innocence. The base rate is the crux.

The thread is a textbook illustration of confusing likelihood with posterior in Bayesian reasoning.

Related event: Lawyer's Flawed Probability Reasoning Sparks Bayesian Debate(2 posts)→

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