Experience in the application of unit roots and fractional difference models and tests

One of the most important aspects in analyzing economic time series is to specify whether the observed series is generated by a stationary or non-stationary process, since most macroeconomic variables could be generated by a unit autoregressive root process. This determination as to whether or not a series should be differenced is known as the unit root test. In other words, if a time series in non-stationary, then in the presence of a unit autoregressive root, it can be converted to a stationary and invertible process by first differencing.