We obtain an inequality for th esmaple varaince of a Brownian motion on [0,1] and an associated Ornstein-Uhlenbeck process. The result is applied to a regression involving a near-integrated regressor, and establishes that in the limit the dispersion of the least squares estimator is greater in...

A sequential procedure for determination of trend degree and testing for unit root is introduced; its properties are investigated by Monte Carlo experiments. We compare the performance of Augmented Dickey-Fuller tests and the GLS tests of Elliott, Rothenberg and Srock (1996), in both cases with lag...

In this paper, we analyse the behaviour of regression-based tests for seasonal unit roots when the error is periodically heteroscedastic. We show, using the case of quaterly data to illustrate, that the limiting null distribution of tests for unit roots at the zero and Nyquist frequencies are...