Screening Test PPV vs Prevalence

A screening test's sensitivity and specificity are fixed properties of the test, but its positive predictive value — the chance a positive result is actually correct — depends heavily on how common the condition is in the population being screened. This simulator tests a live 3D population of simulated people with adjustable sensitivity, specificity and disease prevalence, color-codes every true positive, false positive, false negative and true negative, and reports the live PPV so you can watch it swing from confidently high to surprisingly low at the same fixed test accuracy.