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Bayes theorem, the geometry of changing beliefs

A 15-minute video by 3Blue1Brown about computing mechanisms, probability and information and mathematical reasoning, on the Statistics shelf. It came up in 2 Reddit threads, in r/3Blue1Brown and r/math. It is pitched at introductory level.

3Blue1Brown, Video, 15 min, 2019, on the Statistics shelf

Perhaps the most important formula in probability.

Study notes

Introductory, Visual intuition. Step 2 of 11 in From probability to modern AI

Helpful first

• Fractions
• Basic probability

What it builds

• Recognize which facts are relevant to an estimate.
• Distinguish a base rate from a conditional probability.
• Update a probability using evidence.

Useful moments

• 3:06Recognizing relevant facts
• 3:55Working through the librarian example

Check yourself: Why can a positive test result be misleading when the underlying condition is rare?

Next in the path: Why “probability of 0” does not mean “impossible” | Probabilities of probabilities, part 2

Notes are based on metadata, Reddit context and selected English caption passages. They are not a review of every claim in the video.