Definitive Screening Design for Eight Three-Level Factors shows an example of a definitive design with eight three-level factors. Notice that each pair of rows is a foldover pair; each even-numbered row mirrors the previous row. This foldover design removes the confounding of two-factor interactions and main effects. Each column includes three zero values, which means that quadratic effects are estimable in each factor. And the center run in the last row enable you to include all main effects, quadratic effects for each factor, and an intercept term in the model.