Testing for Unit Roots: What Should Students Be Taught?

Unit-root testing strategies are unnecessarily complicated because they do not exploit prior knowledge of the growth status of the time series, they worry about unrealistic outcomes, and they double- or triple-test for unit roots. The authors provide a testing strategy that cuts through these complications and so facilitates teaching this dimension of the unit-root phenomenon. F tests are used as a vehicle for understanding, but t tests are recommended in the end, consistent with common practice.