A test is 95% accurate. You test positive. What's the probability you have the disease? Adjust base rates and test accuracy to see how beliefs update.
Choose Scenario
A rare disease affects 1 in 1000 people. A test is 95% accurate. You test positive.
Base Rate
0.1%
Sensitivity
95%
Result
POSITIVE
Your intuitive guess
If the test is positive, what's the probability the person actually has the disease?
P(Has Disease | Test Positive)
Ready to see the math?
Lock in your guess above first, then reveal the actual posterior probability.