Empirical studies have shown little evidence to support the presence of all unit roots present in the filter in quarterly seasonal time series. This paper analyses the performance of the Hylleberg, Engle, Granger and Yoo (1990) (HEGY) procedure when the roots under the null are not all present....

Several unit root tests in panel data have recently been proposed. The test developed by Harris and Tzavalis (1999 JoE) performs particularly well when the time dimension is moderate in relation to the cross-section dimension. However, in common with the traditional tests designed for the...

This paper proposes a test statistic for the null hypothesis of panel stationarity that allows for the presence of multiple structural breaks. Two different specications are considered depending on the structural breaks affecting the individual effects and/or the time trend. The model is exible...

In the present paper we study the effects in econometric inference when ussing seasonal adjusted data obtained by signal extraction filters. In particular we analyze the effects in the integration order in zero frequency of the adjusted series. We center our study in the consequences of the...

This paper examines the implications of applying the Hylleberg, Engle, Granger, and Yoo (1990, <italic>Journal of Econometrics</italic> 44, 215–238) (HEGY) seasonal root tests to a process that is periodically integrated. As an important special case, the random walk process is also considered, where the...

This paper examines the effect of X-11 seasonal adjustment on periodic autoregressive processes, using both analytic techniques and simulation. Analytical results show that adjustment reduces (but does not eliminate) periodicity in the coefficients of a stationary PAR(1) process, and it...

The contribution of this paper is three-fold. Firstly, a characterisation theorem of the sub-hypotheses comprising the seasonal unit root hypothesis is presented which provides a precise formulation of the alternative hypotheses against which regression-based seasonal unit root tests test....

Empirical studies have shown little evidence to support the presence of all unit roots present in the Delta_4 filter in quarterly seasonal time series. This paper analyses the performance of the Hylleberg, Engle, Granger and Yoo [Journal of Econometrics (1990) Vol. 44, pp. 215-238] (HEGY)...