On the extendibility of partially exchangeable random vectors

Von Plato (1991) has recently proposed a necessary condition for the infinite extendibility of a partially exchangeable {0, 1}-valued random vector. This paper will prove necessary conditions for the finite extendibility (of any order) of a partially exchangeable process of real-valued (not necessarily {0, 1}-valued) random variables. These conditions will be expressed in terms of the correlation of the random variables. The infinite extendibility condition will be obtained by passing to the limit.