Confident uncertainty believability Frequentist, assume that probability is the long-run frequency of events. Bayesians interpret a probability as measure of belief, or confidence, of an event occurring. We denote our belief about event (A) as (P(A)). We call this quantity the prior probability. “When the facts change, I change my mind.”—John Maynard Keynes Bayesian updates his or her belief after seeing evidence. We denote our updated belief as (P(A|X)), interpreted as the probability of (A) given the evidence …