Prior probability (base rate)

The known or initial frequency with which a given characteristic or event appears in a class of objects or members of a population – data pertaining to the typical or ordinary frequency with which an event occurs in a particular group or in the general population.

(see also: Base rate fallacy, Bayes' theorem, Law of large numbers, Diagnosticity, heuristics (judgemental), Availability heuristic, Representative heuristic, Anchoring effect, Availability, Salience, Vividness, Representativeness, judgement, Conjunction fallacy, Law of large numbers, 'Law of small numbers', Regression towards the mean, actuarial prediction, Prospect theory, endowment effect, decision-making, Decision analysis, decision-making under uncertainty, bounded rationality, bias)