Bayesian Posterior Probability

Update the probability of a hypothesis based on new evidence and base rates.

Why Bayes Matters in Diagnostics

Human intuition often falls victim to the "base rate fallacy." Even with a highly accurate test (e.g., 95% sensitivity and 95% specificity), if a disease is extremely rare (e.g., 1% prevalence), a positive test result still means the patient is more likely to be healthy than sick. This calculator instantly reveals the true predictive value.