Inconsistency of a Unit Root Test Against a Stochastic Unit Root Process

Abstract

In this article, we develop the asymptotic theory of Hwang and Basawa (2005) for explosive random coefficient autoregressive (ERCA) models. Applying the theory, we prove that a locally best invariant (LBI) test in McCabe and Tremayne (1995), which is for the null of a unit root (UR) process against the alternative of a stochastic unit root (STUR) process, is inconsistent against a class of ERCA models. This class includes a class of STUR processes as special cases. We show, however, that the well-known Dickey-Fuller(DF) UR tests and a LBI test of Lee (1998) are consistent against a particular case of this class of ERCA models.