Alias Terms

In the custom design Alias Terms section, add potentially active effects that are not in your assumed model but might bias the estimates of model terms. It is possible that effects not included in your assumed model are active. Once you generate your design, the Alias Matrix section appears under Design Evaluation. The Alias Matrix entries represent the degree of bias imparted to model parameters by the effects that you specified in the Alias Terms section. See the “The Alias Matrix”.

By default, the Alias Terms section includes all two-way interaction effects that are not in your Model section (with the exception of terms involving blocking factors). Add terms using the buttons. For a description of how to use these buttons to add effects to the Alias Terms table, see Model.

Note: For interaction terms, only interactions of the selected order are added. This differs from the Model section where interactions of the selected order and all lower orders are added to the model.

For example, suppose that you specify a design with three continuous factors. Your assumed model, specified in the Model section, contains only those three main effects. You can afford only six runs. You want to see how estimates of the main effects might be biased by active two-way interactions and the three-way interaction.

The Alias Terms table includes all two-way interactions by default. You can add the three-way interaction by selecting Interactions > 3rd.

Figure 4.21 Alias Terms 

Once you specify six runs in the Design Generation section and click Make Design, the Design Evaluation section appears. Open the Design Evaluation section and the Alias Matrix section.

Figure 4.22 Alias Matrix 

The Alias Matrix indicates that each main effect is aliased with one of the interactions. See “Alias Matrix” and “The Alias Matrix”.