Ch. 23 Cointegration 1 Introduction An important property of (1) variables is that there can be linear combinations of theses variables that are I(O). If this is so then these variables are said to be cointegrated. Suppose that we consider two variables Yt and Xt that are I(1) (For example, Yt= Yt-1+ St and Xt= Xi-1+nt.)Then, Yt and Xt are said to be cointegrated if there exists a B such