A modified LLC panel unit root test of the PPP hypothesis

In a recent study, Westerlund (Empir Econ 37:517–531, <CitationRef CitationID="CR37">2009</CitationRef>) shows that the performance of the popular LLC (Levin et al., J Econ 108:1–24, <CitationRef CitationID="CR22">2002</CitationRef>) panel unit root test depends critically on the choice of lag truncation used when correcting for serial correlation, and that it is only when this parameter is set as a function of time that the power raises above size. The purpose of the current paper is to propose a modified test that does not suffer from this drawback. The new test is not only simpler to compute but also superior in terms of small-sample performance, which is illustrated using an example purchasing power parity for less developed countries. Copyright Springer-Verlag 2013