Bayesian
Courtroom

Weigh the evidence. Decide the verdict.
How certain must you be?

or
How to Play

Imagine you hear a noise outside. Before looking, you might think there's a 10% chance it's a deer — that's your prior probability.

Then you see hoof prints. That's evidence. Hoof prints are very likely if it's a deer, and unlikely if it's a cat. So your belief that it's a deer goes up.

In this game, you're a juror. You start with a base rate — how likely is it that any random person committed the crime? Then you evaluate each piece of evidence:

  • How likely is this evidence if the defendant is guilty?
  • How likely is this evidence if the defendant is innocent?

Each answer shifts your belief. At the end, you'll see whether the evidence meets your personal standard for conviction.

We measure evidence in decibels (dB) — a way to add up how strong or weak each piece of evidence is. Positive dB pushes toward guilt; negative dB pushes toward innocence.

Choose a Case

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Set Your Standard

Before you see the case, decide how certain you need to be to convict. What false-conviction rate can you accept?

Your conviction threshold: 20.0 dB

Game Lobby

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Starting Point: Prior Probability

Evidence Overview

0% Innocent 100% Guilty
550%
550%
Likelihood ratio 1.00
dB update 0.0 dB
New cumulative probability

0% 100%
View Detailed Results