Using Monte Carlo simulation, threshold autoregressive (TAR) and momentum-threshold autoregressive (MTAR) asymmetric unit root tests are examined in the presence of generalised autoregressive conditional heteroskedasticity (GARCH). It is shown that TAR and MTAR unit root tests exhibit greater...

The standard Dickey–Fuller (DF) test is routinely employed to analyse the integrated nature of economic and financial time series. However, recent research has shown the test to suffer severe size distortion in the presence of breaks in innovation variance under the unit root null hypothesis....

Much attention has been paid in recent years to the study of the order of integration of a time series, i.e. the number of differences that are necessary to transform it into a stationary series. The relevance of the subject arises because most of time series analysis in economics and finance...