Fit General Linear Model - Model
main topic     see also 

Stat > ANOVA > General Linear Model > Fit General Linear Model > Model

Use to add interaction terms and polynomial terms to your model. By default, the model contains only the factors and covariates that you entered in the main dialog box. Click Default, to return to this model at any time.

Terms in the model displays nested factors using parentheses. For example, when Operator is nested in Plant, Minitab displays Operator (Plant).

To add terms to the model, select at least one factor, covariate, or term. To select multiple items, press the Ctrl key while you click the variables and/or terms.

There are three basic ways that you can add terms. Under Dialog box items, we use examples to illustrate them. For the examples, assume the Factors and covariates list has 3 continuous variables, X, Y, Z and 2 categorical variables, A, B.

Dialog box items

Add terms using selected factors, covariates, and model terms:

Interactions through order: This option adds all interactions through the specified order. Suppose you select variables  X, Y, A and interactions through order 3. When you click Add, Minitab adds X*Y, X*A, Y*A, X*Y*A.

Terms through order: Use to model curvature. This option adds powers and interactions through the specified order. Powers are only for covariates. Suppose you select  X, Y, Z and terms through order 3. When you click Add, Minitab adds X*X,  Y*Y, X*Y, X*X*X,  Y*Y*Y, X*X*Y, X*Y*Y.

Cross factors, covariates, and terms in the model: This option can be used in several ways.

1    You can cross two or more factors and covariates. Suppose you select X, Y, Z. When you click Add, Minitab adds X*Y*Z.

2    You can cross two or more terms that are already in the model.  Suppose X*A and X*B are in the model. If you select these terms and click Add, Minitab adds X*X*A*B.

3    You can cross factors and covariates with terms that are already in the model. Suppose X*X and Y*Y are in the model. If you select these terms and factors A, B then click Add, Minitab adds X*X*A,  X*X*B, Y*Y*A,  Y*Y*B,   Note, each factor is crossed with each model term.

Default: Populates the model with only the factors and covariates that you entered in the main dialog box.

Delete Terms:  You can delete one or more terms from the model. Select the terms and click the Delete button in the dialog. You can also double-click a term to delete it.

Reorder Terms: When you add terms, they are put at the end of the list of model terms. To move a term, select it then click one of the arrow buttons in the dialog to move the term up or down. You can also move a contiguous block of terms. Click the first then Shift and click the last term to select the whole block. Then click the appropriate arrow to move the block.