Let
equation be the
observation at the
,
, and
levels of A, B, and C respectively, where s = 0, 1,..., L 1. Express each observation as the sum of eight components. Thus,

where
is the overall mean.
is the average effect of the
level of factor A.
is the average effect of the
level of factor B.
is the average effect of the
level of factor C.
is the two-factor interaction of the
level of factor A with the
level of factor B.
is the two-factor interaction of the
level of factor A with the rth level of factor C.
is the two-factor interaction of the
level of factor B with the rth level of factor C.
is the three-factor interaction of the
level of factor A, the
level of factor B, and the
level of factor C.
is random fluctuation.