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
(Billingsley 1986) to approximate the variancecovariance matrix of
the constituent expressions.
The following option is available in the CONTRAST statement.
 DF=d

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.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.