Split-plot designs with mirror image pairs as sub-plots

► We discuss two-level split-plot designs with mirror image pairs as sub-plots. ► For these, sub-plot main effects and sub-plot by whole-plot interactions can be estimated separated from the rest. ► These designs can be analyzed by means of a two step OLS procedure. ► Tables with designs of projectivity greater or equal to 3 are given and ways of construction are provided. ► Designs constructed from non-regular designs have better projection properties compared to run size.