Upper and lower probabilities

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Upper and lower probabilities are representations of imprecise probability. Whereas probability theory uses a single number, the probability, to describe how likely an event is to occur, this method uses two numbers: the upper probability of the event and the lower probability of the event.

Because frequentist statistics disallows metaprobabilities, frequentists have had to propose new solutions. Cedric Smith and Arthur Dempster each developed a theory of upper and lower probabilities. Glenn Shafer developed Dempster's theory further, and it is now known as Dempster-Shafer theory.

There are many formal correspondences between upper and lower probability and possibility theory. For example, necessity can be seen as a lower probability and possibility can be seen as an upper probability.

Upper and lower probabilities

See also