Better Foldover Fractions for Resolution III 2k-p Designs

This article describes a family of Resolution IIIdesigns for which the usual advice regarding foldover—reversing all factors—is ill advised. The smallest such designs have 16 runs. For designs in this family, alternative foldover fractions not only increase the resolution to IV, but also separate some of the aliased two-factor interactions. Although Resolution IV designs obtained by reversing all factors provide fewer than half the degrees of freedom for estimating two-factor interactions, the recommended foldovers for designs in this class permit estimation of many more two-factor interactions. This result implies that designs in this class make attractive initial designs, even if they are not minimum aberration.