Pairwise independence

Uncertain variables, U₁, ..., U_n, are said to be pairwise independent if knowing the outcome of any one of those variables provides no information about the outcome of any other. Pairwise independence is a significantly weaker condition than mutual independence and, in particular, does not imply that the joint probability distribution of the set of uncertain variables is equal to the product of their marginal probability distributions. In practice, most assertions of independence result from an underlying understanding of the behavior of the variables being represented.