Specify what to do with a non-hierarchical model and the treatment of hierarchy when you use stepwise selection. The changes you make to the defaults remain until you change them again, even after you exit Minitab.
- What to do when the specified model is non-hierarchical
- Prompt me: Minitab displays a dialog box to ask whether to use a non-hierarchical model or to make the model hierarchical.
- Add terms to make the model hierarchical: Minitab adds the displayed terms to produce a hierarchical model.
- Use the specified non-hierarchical model: Minitab doesn't add the terms.
- Model hierarchy in Stepwise
- Hierarchical model requirement if potential terms are hierarchical
If you require a hierarchical model, choose the types of terms that must be hierarchical.
- Require a hierarchical model at each step: Minitab can add or remove only terms that maintain hierarchy.
- Add terms at the end to make the model hierarchical: Initially, Minitab follows the standard rules of the stepwise procedure. At the final step, Minitab adds the terms that produce a hierarchical model, even if their p-values are greater than the alpha-to-enter.
- Do not require a hierarchical model: The final model can be non-hierarchical. Minitab adds and removes terms based only on the rules of the stepwise procedure.
- Terms affected by the hierarchical model requirement
- All terms: Terms that include continuous and/or categorical variables must be hierarchical.
- Terms with categorical predictors: Only terms that include categorical variables must be hierarchical.
- How many terms can enter if requiring hierarchy at each step
If you require hierarchy at each step, choose the number of terms that Minitab can add at each step in order to maintain hierarchy.
- At most one term can enter at each step: A higher-order term can enter the model only if hierarchy is maintained when adding that single term. All lower-order terms that comprise the higher-order must already be in the model.
- Extra terms can enter to maintain hierarchy: A higher-order term can enter the model even if it produces a non-hierarchical model. However, the terms that are necessary to produce a hierarchical model are also added, even if their p-values are greater than the alpha-to-enter.