Foldovers of 2^k-p resolution IV experimental designs

Two simple rules are used to develop foldovers for 2^k-p fractional factorial designs. Although the rules are general, our focus is on foldovers for resolution IV designs. Foldovers that sign-reverse more than one factor can generate alias sets that cannot be obtained from a sign-reversal of a single factor. The potential alias structure can be limited by widely-used statistical software. An example illustrates the interplay of the rules and information from active alias sets in the original fractional experiment.