Bayes' Theorem

How should a test result change what you believe? Count the people: when a condition is rare, most positive tests come from the healthy majority, however good the test.

Step 1 of 13

sick, tests positivesick, missedhealthy, false positivehealthy, negative

Speed

A town of 1,000 people. A condition affects 1% of them, and there is a test for it. Each dot is a person.

The formula fills in once everyone has been tested.

Sick (base rate)10 of 1000 (1%)Sensitivity P(+ | sick)90%False positives P(+ | healthy)9%

DSAverse

Bayes' Theorem

See also

Bayes' Theorem

See also