EXPECTATION, in the doctrine of chances, is applied to any contingent event, and is capable of being reduced to the rules of computation. Thus a sum of money in expectation when a particular event happens, has a determinate value before that event arrives; so that if a person is to receive any sum, say L.10, when an event takes place which has an equal probability of happening and failing, the value of the expectation is half that sum, or L.5; and in all cases the expectation of obtaining any sum is estimated by multiplying the value of the sum expected by the fraction which represents the probability of obtaining it. The expectation of a person who has three chances in five of obtaining L.100, is equal to , or L.60, and the probability of obtaining L.100 in this case is equal to . See PROBABILITIES.
EXPECTATION OF LIFE signifies that share or number of the years of human life which a person of any given age may expect to enjoy upon an equality of chances. See ANNUITIES.