The clinic

A person tests positive. Drag the base rate and the two error rates. The posterior is Bayes’ theorem, not the true-positive rate.

Prevalence1%True positive rate99%False positive rate5%

Likelihood of + if ill

0.99

Posterior of illness given +

0.167

P (D ∣ T^{+}) = \frac{0.99 \cdot 0.010}{0.99 \cdot 0.010 + 0.05 \cdot 0.990}