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
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- 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
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- Hierarchical model requirement if potential terms are hierarchical
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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
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- 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
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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.
