Prior Knowledge
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.
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. Browse all games →
