a formula for calculating the probability that an event will occur that allows for the acquisition of new information regarding that event. For example, consider the probability that an individual will have a stroke within the next year. Using Bayes theorem, one could take an estimate of this probability based on general population data for that individual’s age group (i.e., the prior probability) and revise it to account for the results of that person’s stress tests and other cardiological markers, creating what is known as the posterior probability. [Thomas Bayes]