ABSTRACT
In Chapters 3 and 4 we presented the simplest of factorial experiments, namely those with only two levels for each of the factors under study. Examples of two-level factorials were shown when the factors were quantitative such as moisture %, or qualitative such as thread type (rolled or tapped). It makes sense to use two levels for quantitative factors if we are interested in linear relationships. However, two levels are only appropriate for qualitative factors when there are just two alternatives. In many practical situations there may be more than two alternatives for qualitative factors, such as component type A, B, C, or D in a prototype, or material types 1, 2, or 3. Also, it may be desirable to study nonlinear relationships for quantitative factors. Chapters 9-11 of this book present experimental designs specifically for studying nonlinear relationships when only quantitative factors are present. In this chapter we study an extension of the factorial experiments that we have already presented in Chapters 3 and 4.
