SAS/STAT 922 User's Guide: The MIXED Procedure (Book Excerpt)

4522 ✦ Chapter 56: The MIXED Procedure
The statements to fit this correlation model in PROC MIXED are as follows:
proc mixed;
class Family Gender;
model Height = Gender;
random Family Family*Gender;
run;
Note that Family and Family*Gender are now listed in the RANDOM statement. The dummy variables
associated with them are used to construct the Z matrix in the mixed model. The X matrix now
consists of a column of 1s and the dummy variables for Gender.
The G matrix for this model is diagonal, and it contains the variance components for both Family and
Family*Gender. The R matrix is still assumed to equal 2 I, where I is an identity matrix.
The output from this analysis is as follows.
Figure 56.8 Model Information
The Mixed Procedure
Model Information
Data Set WORK.HEIGHTS
Dependent Variable Height
Covariance Structure Variance Components
Estimation Method REML
Residual Variance Method Profile
Fixed Effects SE Method Model-Based
Degrees of Freedom Method Containment
The “Model Information” table in Figure 56.8 shows that the containment method is used to compute
the degrees of freedom for this analysis. This is the default method when a RANDOM statement is
used; see the description of the DDFM= option for more information.
Figure 56.9 Class Level Information
Class Level Information
Class Levels Values
Family 4 1 2 3 4
Gender 2 F M
The “Class Level Information” table in Figure 56.9 is the same as before. The “Dimensions” table in
Figure 56.10 displays the new sizes of the X and Z matrices.