Resolution of a fractional factorial design ($R={\min }_{G\in \mathcal{H}\setminus \{I\}}|G|$)

The resolution of a regular fraction is the shortest nonidentity word in its defining contrast subgroup. Two effects alias only when their word product belongs to that subgroup. Thus resolution VI separates all main effects and two-factor interactions from one another and from three-factor interactions, though some three-factor interactions alias in complementary pairs.