The DDFM=CONTAIN method is carried out as follows: Denote the fixed effect in question as A
and search the G-side random effect list for the effects that syntactically contain A
. For example, the effect B
(A
) contains A
, but the effect C
does not, even if it has the same levels as B
(A
).
Among the random effects that contain A
, compute their rank contributions to the matrix (in order). The denominator degrees of freedom that is assigned to A
is the smallest of these rank contributions. If no effects are found, the denominator degrees of freedom for A
is set equal to the residual degrees of freedom, . This choice of degrees of freedom is the same as for the tests performed for balanced split-plot designs and should be adequate
for moderately unbalanced designs.
Note: If you have a matrix with a large number of columns, the overall memory requirements and the computing time after convergence can be substantial for the containment method. In this case, you might want to use a different degrees-of-freedom method, such as DDFM=RESIDUAL, DDFM=NONE, or DDFM=BETWITHIN.