Generating the Intrablock and Interblock Subgroups for Confounding in General Factorial Experiments

A simple method of directly obtaining generators for the intrablock subgroup and for the interblock subgroup of a confounding plan is presented. The method is applicable to completely general factorial experiments and can be used either to construct the design which confounds a specified set of treatment effects or to determine the confounding pattern of a specified design. This procedure avoids the usual trial and error approach to confounding and involves nothing more complicated than addition and multiplication modulo a prime number.