A NOTE ON THE DEFINITION OF RESOLUTION FOR BLOCKED 2(K-P) DESIGNS

When two-level fractional factorial designs are blocked, the application of the standard definition of resolution requires careful consideration. Sometimes linear contrasts that superficially appear to be estimates of higher-order interaction effects are in reality estimates of first-order effects. Experimenters may therefore inadvertently choose designs that are of lower resolution than intended or unknowingly confound important effects. In this note, I discuss this subtle problem and propose an additional rule to the usual definition of resolution that provides a conservative but more realistic assessment of the resolution. With this more realistic characterization, experimenters are provided with a warning about possible confounding. I also show that my amendment to the definition of resolution may be useful when characterizing designs in which several two-level contrasts are combined to accommodate factors with four or more levels.