In this paper we derive, under the assumption of Gaussian errors with known errorcovariance matrix, asymptotic local power bounds for seasonal unit root tests for bothknown and unknown deterministic scenarios and for an arbitrary seasonal aspect. Wedemonstrate that the optimal test of a unit...

In this paper we develop a simple procedure which delivers tests for the pres-ence of a broken trend in a univariate time series which do not require knowledgeof the form of serial correlation in the data and are robust as to whether theshocks are generated by an I(0) or an I(1) process. Two...