Which terms should I fit in a response surface design?

The model you choose determines what terms are fit and whether or not you can model linear or curvilinear aspects of the response surface. If you include any second-order terms (squares or interactions), you can model curvilinear data.

To save time in model specification, you can choose a model type in the Terms sub-dialog box so that Minitab fits a certain set of terms. The following table shows what terms Minitab fits for each model type.

Model type Terms
Linear A B C D
Linear and squares A B C D A*A B*B C*C D*D
Linear and 2-way interactions A B C D A*B A*C A*D B*C B*D C*D
Full quadratic (default) A B C D A*A B*B C*C D*D A*B A*C A*D B*C B*D C*D

You can add or remove terms from any of these sets to specify the exact model that you want.

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