Cognitive Scaffold

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MENTAL MODEL · M2921

The Prosecutor's Fallacy

The Prosecutor's Fallacy
TechnicalHigh supportProbability Theory
Included
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Version 1.0.0 · Updated 2026-07-30

CORE DEFINITION

The erroneous belief that a low probability of evidence given innocence (P(evidence|innocent)) is equivalent to a low probability of innocence given the evidence (P(innocent|evidence)). - Example: The probability of a DNA match error is one in a million. The prosecutor says: 'So the probability he is innocent is only one in a million.' (Wrong! If there are 10 million people in the city, perhaps 10 people match, and the probability he is the culprit is actually only 1/10). -

SCAFFOLDING EFFECT

psychology

Reduce cognitive load

A fatal confusion of conditional probabilities. - This is the mathematical source of wrongful convictions. When doing A/B testing or attribution analysis.

anchor

Anchor fast decisions

The prosecutor mistakenly treats the probability of evidence given guilt as the probability of guilt given evidence, confusing the direction of conditional probability and leading to misjudgment.

MINIMUM ACTION

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Source support: Explicit

  • link
    zh.wikipedia.orghttps://zh.wikipedia.org/wiki/%E6%AA%A2%E5%AF%9F%E5%AE%98%E8%AC%AC%E8%AA%A4ZH · Explicit
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