Two methods for choosing a follow-up experiment are: (i) Fold-over technique. Choose the second design by switching the signs of some or all columns in the first design. Its objectives are more narrow...

Two methods for choosing a follow-up experiment are:

(i) Fold-over technique. Choose the second design by switching the signs of

some or all columns in the first design. Its objectives are more narrow and

the method is less flexible than the optimal design approach.

(ii) Optimal design approach. Apply an optimal design criterion like the D or

Ds criterion to a model consisting of the effects (including all its aliases)

identified as significant in the original experiment. It works for any model

and shape of experimental region. By using fast optimal design algorithms,

it can be used to solve large design problems.