A BY statement can be used with PROC PANEL to obtain separate analyses on observations in groups defined by the BY variables. When a BY statement appears, the input data set must be sorted by the BY variables as well as by cross section and time period within the BY groups.

The following statements show an example:

   proc sort data=a;
      by byvar1 byvar2 csid tsid;
   run;

   proc panel data=a;
      by byvar1 byvar2;
      id csid tsid;
      ...
   run;