Mixed two- and four-level split-plot designs with combined minimum aberration

When the levels of some factors in an experiment are difficult to be changed or controlled, fractional factorial split-plot (FFSP) designs are commonly used in which the factors are classified as the whole plot (WP) and sub-plot (SP) factors. Mixed-level designs are used in practice when the levels of the factors are not equal to each other. This paper considers the mixed-level FFSP designs with the WP factors being more important than the SP factors. It proposes the combined minimum aberration criterion of type WP (WP-MA $$^{c}$$ ) for mixed-level FFSP designs. Some optimal mixed-level FFSP designs are constructed under the WP-MA $$^{c}$$ criterion.