The essential equivalence of pairwise and mutual conditional independence

Abstract

For a large collection of random variables, pairwise conditional independence and mutual conditional independence are shown to be essentially equivalent - i.e., equivalent to up to null sets. Unlike in the finite setting, a large collection of random variables remains essentially conditionally independent under further conditioning. The essential equivalence of pairwise and multiple versions of exchangeability also follows as a corollary. Our result relies on an iterated extension of Bledsoe and Morse's completion of the product of two measure spaces.