Using Predictor Variables
Fitting the Intervention Model
The Interventions for Series window now contains definitions for four intervention predictors. Select all four interventions, as shown in Figure 21.
Figure 21: Interventions for Series Window
Click the OK button. This returns you to the ARIMA Model Specification window, which now lists items in the Predictors list, as shown in Figure 22.
Figure 22: Linear Trend with Interventions Specified
Click the OK button to fit this model. After the model is fit, bring up the Model Viewer. You will see a plot of the model predictions, as shown in Figure 23.
Figure 23: Linear Trend with Interventions Model
You can use the Zoom In feature to take a closer look at how the complex intervention effect fits the excursion in the series starting in August 1990.