Abstract
Abstract This article proposes tests for unit root and other forms of nonstationarity that are asymptotically locally most powerful against a certain class of alternatives and have asymptotic critical values given by the chi-squared distribution. Many existing unit root tests do not share these properties. The alternatives include fractionally and seasonally fractionally differenced processes. There is considerable flexibility in our choice of null hypothesis, which can entail one or more integer or fractional roots of arbitrary order anywhere on the unit circle in the complex plane. For example, we can test for a fractional degree of integration of order 1/2; this can be interpreted as a test for nonstationarity against stationarity. “Overdifferencing” stationary null hypotheses can also be tested. The test statistic is derived via the score principle and is conveniently expressed in the frequency domain. The series tested are regression errors, which, when the hypothesized differencing is correct, are w...
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call