Recent developments in the design of field experiments. I. Split-plot confounding

A convenient method of introducing into a field experiment additional factors which can be applied to smaller areas than that of the whole plots is to use split plots: each whole plot is split into sections, and the different combinations of the additional factors are randomized over each set of sub-plots. An extension of this idea is the device of split-plot confounding, by which not all the combinations of the additional factors are used in every whole plot; instead, the possible combinations are subdivided into two or more sets which are then assigned to blocks and whole-plot treatments in a balanced manner, in such a way as to confound certain interactions of the additional factors between whole plots and certain higher order interactions between blocks.