SAS/STAT 9.2 User's Guide: The MIXED Procedure (Book Excerpt)

3922 ✦ Chapter 56: The MIXED Procedure
SINGULAR=number
tunes the estimability checking as documented for the SINGULAR= option in the
CONTRAST statement.
SLICE= fixed-effect
SLICE= (fixed-effects)
specifies effects by which to partition interaction LSMEANS effects. This can produce what
are known as tests of simple effects (Winer 1971). For example, suppose that A*B is significant,
and you want to test the effect of A for each level of B. The appropriate LSMEANS
statement is as follows:
lsmeans A*B / slice=B;
This code tests for the simple main effects of A for B, which are calculated by extracting the
appropriate rows from the coefficient matrix for the A*B LS-means and by using them to form
an F test. See the section “Inference and Test Statistics” for more information about this F
test.
The SLICE option produces a table titled “Tests of Effect Slices.” For ODS purposes, the
table name is “Slices.”
MODEL Statement
MODEL dependent = < fixed-effects >< / options > ;
The MODEL statement names a single dependent variable and the fixed effects, which determine the
X matrix of the mixed model (see the section “Parameterization of Mixed Models” on page 3975
for details). The specification of effects is the same as in the GLM procedure; however, unlike
PROC GLM, you do not specify random effects in the MODEL statement. The MODEL statement
is required.
An intercept is included in the fixed-effects model by default. If no fixed effects are specified, only
this intercept term is fit. The intercept can be removed by using the NOINT option.
Table 56.6 summarizes options in the MODEL statement. These are subsequently discussed in
detail in alphabetical order.
Table 56.6 Summary of Important MODEL Statement Options
Option Description
Model Building
NOINT excludes fixed-effect intercept from model
Statistical Computations
ALPHA=˛ determines the confidence level (1 ˛) for fixed effects
ALPHAP=˛ determines the confidence level (1 ˛) for predicted values
CHISQ requests chi-square tests
DDF= specifies denominator degrees of freedom (list)