Spurious Rejections with Endogenous Break Unit Root Tests in the Presence of Outliers and Breaks

摘要

Unit root tests with structural break developed by Zivol and Andrews (1992) and Perron and Rodriguez (2003) in the presence of additive outliers and breaks are studied by simulation experiments. The results show that the Zivot-Andrews test appears to have size distortions due to the additive outliers whereas the Perron-Rodriguez test exhibits good properties of size and power. However, the two tests are biased when a second break is present but not taken into account. Furthermore, these endogenous break unit root tests tend to determine the break point incorrectly at one period behind the true break point, leading to spurious rejections of the unit root null hypothesis.