2. According to the specific situation of the sequence, for example, you can draw a line chart in excel to observe the trend of lines. If the image has obvious trend and intercept, the trend and intercept will be selected in ADF test.
3. If it is stable, the regression model can be established directly. If it is unstable, it can be used as a first-order difference to see if it is stable. If it is still unbalanced, it can be used as a second-order difference. Many economic variables are unstable, but the difference series is often stable.
4. After the test, there will be the term "prob" (that is, adjoint probability). If the confidence level is 5%, as long as prob is less than 5%, the sequence is stable, otherwise there is a unit root.
5. If there is a unit root, it is recommended to take the natural logarithm. You can directly enter genr y=log () in the command window, and then press enter. Fill in the brackets with the name of the sequence to be logarithm.