A procedure for updating the probability of an event based on new knowledge (when new evidence is gathered). In its simplest form, it can be written as conditional probabilities using the formulaBayes formula The theorem gives the probability Bj, when the probability A is known. The quantity Pr(Bj) is called the a priori probability, and Pr(Bj|A) the a posteriori probability. The relationship between prior and posterior probabilities is given by the formulaApriori and posterior probabilities in Bayes' formula