Conditional Probability and Base Rate
by Anonymous
Adjust the rarity and the test's accuracy to see that the base rate, not the test, decides how likely a positive result is real.
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About this app
Conditional Probability and Base Rate is an interactive learning app about why a positive test result does not have the same meaning in every population. Using a 10,000-person table, adjustable rarity, sensitivity, and specificity, it shows how the share of true positives changes even when test performance stays at 99%. A curve view and comparison challenge reinforce the role of base rates and false positives.
Use cases
- Students learning conditional probability and Bayes’ theorem
- Adults exploring medical-test statistics and cognitive biases
- Educators demonstrating false positives with an interactive example
- Anyone practicing critical thinking about test accuracy claims
Features
- 10,000-person outcome table showing true and false positives and negatives
- Sliders for prevalence, sensitivity, and specificity
- Curve showing how prevalence changes the share of positive results that are real
- Comparison of identical 99% tests across three prevalence levels
- Guided missions with feedback and a next-step progression
- Optional sound toggle