BY variables ;

A BY statement can be used with PROC SIMLIN to obtain separate analyses for groups of observations defined by the BY variables.

The BY statement can be applied to one or both of the EST= and the DATA= input data set. When a BY statement is used and both an EST= and a DATA= input data set are specified, PROC SIMLIN checks to see if one or both of the data sets contain the BY variables.

Thus, there are three ways of using the BY statement with PROC SIMLIN:

1. If the BY variables are found in the EST= data set only, PROC SIMLIN simulates over the entire DATA= data set once for each set of coefficients read from the BY groups in the EST= data set.

2. If the BY variables are found in the DATA= data set only, PROC SIMLIN performs separate simulations over each BY group in the DATA= data set, using the single set of coefficients in the EST= data set.

3. If the BY variables are found in both the EST= and the DATA= data sets, PROC SIMLIN performs separate simulations over each BY group in the DATA= data set using the coefficients from the corresponding BY group in the EST= data set.