Bayesians, by contrast, allow probabilistic judgments about any situation, regardless of whether any observations have yet occurred. To do this, Bayesians begin by bringing related evidence to statistical determinations. For example, picking a penny up off the street, you’d probably initially estimate a fifty-fifty chance that it would come up heads if you flipped it, even if you’d never observed a flip of that particular coin before. In Bayesian statistics, you can bring such knowledge of base rates to a problem. In frequentist statistics, you cannot.
