The NLMIXED Procedure

CONTRAST Statement

CONTRAST ’label’ expression <, expression> <options> ;

The CONTRAST statement enables you to conduct a statistical test that several expressions simultaneously equal zero. The expressions are typically contrasts—that is, differences whose expected values equal zero under the hypothesis of interest.

In the CONTRAST statement you must provide a quoted string to identify the contrast and then a list of valid SAS expressions separated by commas. Multiple CONTRAST statements are permitted, and results from all statements are listed in a common table. PROC NLMIXED constructs approximate F tests for each statement using the delta method (Cox, 1998) to approximate the variance-covariance matrix of the constituent expressions.

The following option is available in the CONTRAST statement:


specifies the denominator degrees of freedom to be used in computing p values for the F statistics. The default value corresponds to the DF= option in the PROC NLMIXED statement.