Begin with a base rate, then run noisy tests one at a time and revise your belief, beware the false positives that trip up everyone's intuition.
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How to play
Each case has a hidden cause with a known prior (base rate). Run diagnostic tests one by one, each with its own sensitivity and specificity, and update how strongly you believe the cause is present. Set your final belief and lock in. You're scored on how well-calibrated your stated probability is against the Bayes-correct posterior, not just which side you picked.
Low base rates make positive results far less convincing than they feel.
Reveal more tests before committing for a small bonus.
A calibration score and the correct posterior are shown afterward.
Controls
Desktop: drag the belief slider or click the belief bar (arrow keys nudge it), run tests, then lock in.
Phone & tablet: drag the slider and tap the buttons, fully touch-friendly.
Game modes
Daily and Practice modes, each in Easy, Medium or Hard difficulty.
Tips & strategy
With a rare cause, even a positive test may leave the probability low, anchor on the base rate.
Combine tests: each result multiplies into your updated belief.
What you'll learn
Prior Knowledge is a Bayesian-reasoning game about base rates, test accuracy and calibrated belief.
Skills: Bayesian reasoning, base rates, conditional probability, calibration
Best for: older teens (roughly grades 10–12)
For parents & teachers: why base rates matter so much.
About Prior Knowledge
Prior Knowledge is a Bayesian-reasoning game about base rates, test accuracy and calibrated belief. It's an original free browser game built for PlayPendium.
A free, original browser game on PlayPendium. No download, no install.
