This paper examines the asymptotic and finite sample behaviour of the ADF and Phillips-Perron statistics under the presence of a break in the trend function. We prove that the break magnitude affects these two statistics in a similar way, drawing them closer the acceptance zone, the higher the...

This paper studies the behavior of the HEGY statistics for quarterly data, for seasonal autoregressive unit roots, when the analyzed time series is deterministic seasonal stationary but exhibits a change in the seasonal pattern. As a by-product we analyze also the HEGY test for the nonseasonal...

This paper shows that the acceptance of the Zipf's Law may sometimes be the result of a spurious artifact. By way of some Monte Carlo exercises we provide evidence in favour of the fact that the Zipf's law can be spuriously accepted when the variable being studied is generated by a random...

This paper considers the behaviour of the Dickey-Fuller tests when the variable being studied is generated according to Perron's (1989) crash hypothesis. We show that these statistics tend towards the Dickey-Fuller distributions under the null hypothesis and diverge towards -[infinity] under the...

The detection of additive outliers in integrated variables has attracted some attention recently, see e.g. Shin et al. (1996), Vogelsang (1999) and Perron and Rodriguez (2003). This paper serves several purposes. We prove the inconsistency of the test proposed by Vogelsang, we extend the tests...