Chapter Summary:
Basically there is OLS method for estimations procedures. But the underlying assumption for OLS is that the series is stationary. If the underlying assumption is not full fills then the method of OLS is not applicable. For this reason, testing of unit root is at the first step of the analysis in time series. Relying on the general rule of thumb, that past trend followed in the future may leads to inaccurate expectations and inappropriate decisions.
Structural break; changing in the behavior of the series, either it is one time unusual behavior or there is permanent shift in the level of the series. Many a time it happens, that we have a stationary series, but due to structural break in the series, convert the stationary series into the nonstationary one. So, it should be study deeply for the accurate expectations and appropriate decisions.