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.
|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.