MENTAL MODEL · M4690

Condorcet's Jury Theorem

DecideHigh supportDecision Science

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Version 1.0.0 · Updated 2026-07-28

CORE DEFINITION

Condorcet's Jury Theorem (CJT) is a theorem in political science concerning the probability of correctness of collective decisions. The theorem was first proposed by the Marquis de Condorcet in his 1785 work 'Essay on the Application of Analysis to the Probability of Majority Decisions'. The simplest version of the theorem assumes that a group needs to make a decision by majority vote (e.g., in a jury system, jurors vote on whether the defendant is guilty). The outcome of the vote can be correct or incorrect. Each voter has some independent private information, which is correct with probability p, and the voter decides based on p. The correctness of the vote outcome is determined by whether p is greater or less than 1/2.

SCAFFOLDING EFFECT

psychology

Reduce cognitive load

anchor

Anchor fast decisions

If each voter is independent and has a correct probability p > 0.5, then the probability that the majority decision is correct tends to 1 as the number of voters n increases; if p < 0.5, then the more people there are, the more likely the overall decision is wrong. The condition for the wisdom of crowds is that individuals are 'above passing'.

MINIMUM ACTION

In progress 0/1

Practice this model in one real situation:

First assess whether the individual accuracy rate in the field is > 50%. If the professional threshold is high (p < 0.5), use expert/elite decision-making rather than expanding the vote. If p > 0.5, you can safely use majority aggregation to improve accuracy.

Check to track your progress (stored locally)

Learning progress0%

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Source support: Explicit

link
zh.wikipedia.orghttps://zh.wikipedia.org/wiki/%E5%AD%94%E5%A4%9A%E5%A1%9E%E9%99%AA%E5%AE%A1%E5%9B%A2%E5%AE%9A%E7%90%86ZH · Explicit
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