Consider a design. Suppose after running the experiment, the largest observed effects are A + BD, B + AD, and D + AB. You wish to augment the original design with a group of four runs to de-alias these effects.
(a) Which four runs would you make?
(b) Find the variances and covariances of the regression coefficients in the model
(c) Is it possible to de-alias these effects with fewer than four additional runs?