Why is it important that time series are “stationary” and what are the implications of non-stationary on OLS estimates? Outline an approach you could use to make a non-stationary series stationary....

Why is it important that time series are “stationary” and what are the implications of non-stationary on OLS estimates? Outline an approach you could use to make a non-stationary series stationary. Discuss what is meant by cointegration and how you would test for it.