Poisson Regression - Model
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Stat > Regression > Poisson Regression > Fit Poisson Model > Model

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

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

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

See Tips for Creating Terms for more information.

Dialog box items

Add terms using selected predictors and model terms:

Interactions through order: This option adds all interactions through the specified order. Suppose you select predictors  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 for continuous predictors. Suppose you select  X, Y, A and terms through order 3. When you click Add, Minitab adds the power terms for X and Y: X*X,  Y*Y, X*X*X,  Y*Y*Y.  Minitab also adds interactions for the predictor variables and powers: X*Y, X*A, Y*A, X*X*Y, X*Y*Y, X*X*A, X*Y*A, Y*Y*A.

Cross predictors and terms in the model: This option can be used in several ways.

1    You can cross two or more predictors. 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 only these terms and click Add, Minitab adds X*X*A*B.

3    You can cross predictors with terms in the model. Suppose X*X and Y*Y are in the model. If you select these terms and predictors A, B then click Add, Minitab adds X*X*A,  X*X*B, Y*Y*A,  Y*Y*B. Each predictor is crossed with each model term, but the predictors are not crossed with themselves and the model terms are not crossed with themselves.

Default: Populates the model with only the predictor variables 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 the term 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 term then hold the Shift key and click the last term to select the whole block. Then click the appropriate arrow to move the block.

Include the constant term in the model: Check to fit the model with a y-intercept (constant term). Consider fitting a model without the constant only if you remove all insignificant terms from the model and the constant is not significantly different from 0. If you do not include the constant in the correct circumstance, this can improve the fit of the model and the precision of the predicted values.