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The first four lines of page 54 should read as follows. ‘Phillips & Perron (1987) observe that the asymptotic distribution of the ordinary least-squares estimators of the autoregressine parameter in model (5) and its associated t statistic are invariant to whether the model is a random walk with or without drift. By similar reasoning our results for T(α¯1- 1) and associated t statistic…’
A. HALL (Thu,) studied this question.