Equiprobable

From Wikipedia, the free encyclopedia

It has been suggested that this article or section be merged with Equipossible. (Discuss)

This article or section is in need of attention from an expert on the subject.
Please help recruit one or improve this article yourself. See the talk page for details.
Please consider using {{Expert-subject}} to associate this request with a WikiProject

Equiprobability is a philosophical concept in probability theory that allows one to assign equal probabilities to outcomes that are judged to be equipossible or to be "equally likely" (in some sense). The best-known formulation of the rule is Laplace' Principle of Indifference, which states that, when we have no other information than that exactly N events can occur and that they are mutually exclusive, we are justified in assigning each the probability 1/N. While this subjective assignment of probabilities works well for rolling dice and lotteries, it could also lead to the seemly absurd conclusion that the sun is as likely to rise as to not rise tomorrow morning. However, the conclusion that sun is equally likely to rise as it is not rise is only absurd when additionally information is known, such as the laws of gravity and the sun's past history.

Most applications of the concept are effectively applications of circular reasoning, with "equally likely" events being assigned equal probabilities, which means in turn that they are equally likely. Despite this, the notion remains useful in probabilistic and statistical modeling.