The degree of confounding in a two-level fractional design (screening design). A design of resolution III does not confound main effects with one another, but does confound main effects with two-factor interactions. A resolution IV design does not confound main effects and two-factor interactions, but does confound two-factor interactions with other two-factor interactions. A resolution V design does not confound main effects and two-factor interactions with each other, but does confound two-factor interactions with three-factor interactions.