Step 4 -- Choose a Model
Note that the selection of the model and the selection of the design go
hand-in-hand. Each design is created for a particular model.
In STRATEGY for Windows, you must complete the design file before specifying
the model, because our model file tracks more than the mathematical model. It
tells the regression engine which columns are factors and which are responses.
A Quadratic Model: saddles, domes and basins.
An Interaction Model: the twisted plane.
A Main Effects Model: to screen many factors down to the strongest few.
Perhaps add higher order interaction terms and/or cubic terms.