Seasonal Unit Root Tests for Trending and Breaking Series with Application to Industrial Production

Abstract

Some unit root testing situations are more difficult than others. In the case of quarterly industrial production there is not only the seasonal variation that needs to be considered but also the occasionally breaking linear trend. In the current paper we take this as our starting point to develop three new seasonal unit root tests that allow for a break in both the seasonal mean and linear trend of a quarterly time series. The asymptotic properties of the tests are derived and investigated in small-samples using simulations. In the empirical part of the paper we consider as an example the industrial production of 13 European countries. The results suggest that for most of the series there is evidence of stationary seasonality around an otherwise nonseasonal unit root.