Do 3rd order effects help define curvature?
If you have are making a design with a factor you are certain will have a quadratic relationship against a response but you have a wide range, can it be helpful to define a 3rd order model effect for that factor to better identify and model curvature. I work in purification and we often deal with a recovery vs. purity balance. This relationship is usually quadratic around the optimal, where at a l...