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Diagnostic Testing Simulator

From disease screening to spam filters — Bayes' Theorem in action

Current Scenario

Disease screening (rare disease)

A screening test for a rare disease in the general population. The disease is uncommon, but the test is fairly accurate.

Result to interpret

Switch between PPV and NPV to compare positive and negative results.

Step 1: Start with prevalence

Every test starts in a specific population. Prevalence tells us how common the condition is — in this scenario, 1.00% of people have the condition, about 10 out of 1,000.

Whole-number counts in the walkthrough are rounded expected counts.

The Big Question

If the result is positive, what is the chance the condition is actually present?

Answer

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Metric

Positive Predictive Value (PPV)

Complete the walkthrough to calculate the PPV for this scenario.