ABSTRACT
This chapter introduces factorial design—a tool that allows industrial experimenters to experiment on many factors simultaneously. The points for the factorial designs are labeled in a “standard order,” starting with all low levels and ending with all high levels. The full-factorial design allows estimation of all three two-factor interactions as well as of the three-factor interaction. Interactions occur when the effect of one factor depends on the level of the other. The microwave popcorn study nicely illustrates how to display and interpret an interaction. The pattern differs from that for taste, but it again exhibits the nonparallel lines that are characteristic of a powerful two-factor interaction. The one-factor-at-a-time (OFAT) experimenter must replicate runs to provide equivalent power. The end result for a two-factor study is that, to get the same precision for effect estimation, OFAT requires 6 runs versus only 4 for the two-level design.
