See how test accuracy, reliability, and disease rarity interact in medical testing.
How common is the disease in this group?
50 sick vs 950 healthy.
If someone is sick, how likely is the test to find it?
If someone is healthy, how likely is the test to be clear?
33.6%
If the test is positive, this is the chance the patient is actually sick.
True Positives / (True Positives + False Positives)
99.8%
If the test is negative, this is the chance the patient is actually healthy.
True Negatives / (True Negatives + False Negatives)
Breakdown of test results for the 1000 people.
The test says these people might be sick.
Sick people correctly identified.
Healthy people given a false alarm.
The test says these people are likely healthy.
Sick people who were missed (dangerous!).
Healthy people correctly cleared.
Shows how PPV changes as disease becomes more common, holding test accuracy constant.