Reduce the Model

The Actual by Predicted Plot shows that the model is significant. There is no evidence of lack of fit.

Figure 4.10 Actual by Predicted Plot for Full Model 

The Effect Summary report suggests that a number of effects are not significant. In particular, X2*X3 is the least significant effect with a PValue of 0.99563. Next, you will systematically reduce the model using the Effect Summary report interactively.

Figure 4.11 Effect Summary Report 

1. In the Effect Summary report, click X2*X3 and click Remove.

The model updates.

The PValue column in the Effect Summary report indicates that X1*X3 is not significant.

2. Click X1*X3 and click Remove.

The PValue for X3*X3 indicates that it is not significant.

3. Click X3*X3 and click Remove.

4. Click X1*X2 and click Remove.

Notice that X3 is not significant. It is not contained in any higher-order effects, so you can remove it without violating the Effect Heredity principle. See Effect Heredity.

5. Click X3 and click Remove.

Figure 4.12 Effect Summary Report After Reducing Model 

All remaining effects are significant.