The RESTRICT statement specifies linear equality restrictions on the parameters in the previous model statement. There can be as many unique restrictions as the number of parameters in the preceding model statement. Multiple RESTRICT statements are understood as joint restrictions on a model’s parameters. Restrictions on the intercept are obtained by the use of the keyword INTERCEPT.

Currently, only linear equality restrictions are permitted in PROC PANEL. Tests and restriction expressions can only be composed of algebraic operations that involve the addition symbol (+), subtraction symbol (–), and multiplication symbol (*).

The RESTRICT statement accepts labels that are produced in the printed output. RESTRICT statement can be labeled in two ways. A RESTRICT statement can be preceded by a label followed by a colon. This is illustrated in rest1 in the example below. Alternatively, the keyword RESTRICT can be followed by a quoted string.

The following statements illustrate the use of the RESTRICT statement:

   proc panel;
      model y = x1 x2 x3;
      restrict x1 = 0, x2 * .5 + 2 * x3= 0;
      rest1: restrict  x2 = 0, x3 = 0;
      restrict "rest2" intercept=1;
   run;

Note that a restrict statement cannot include a division sign in its formulation.