You can specify a BY statement with PROC SURVEYLOGISTIC to obtain separate analyses on observations in groups defined by the BY variables.

Note that using a BY statement provides completely separate analyses of the BY groups. It does not provide a statistically valid subpopulation (or domain) analysis, where the total number of units in the subpopulation is not known with certainty.

When a BY statement appears, the procedure expects the input data sets to be sorted in the order of the BY variables. The variables are one or more variables in the input data set.

If you specify more than one BY statement, the procedure uses only the latest BY statement and ignores any previous ones.

If your input data set is not sorted in ascending order, use one of the following alternatives:

• Sort the data by using the SORT procedure with a similar BY statement.

• Use the BY statement option NOTSORTED or DESCENDING. The NOTSORTED option does not mean that the data are unsorted, but rather that the data are arranged in groups (according to values of the BY variables) and that these groups are not necessarily in alphabetical or increasing numeric order.

• Create an index of the BY variables by using the DATASETS procedure.

For more information about the BY statement, see SAS Language Reference: Concepts. For more information about the DATASETS procedure, see the Base SAS Procedures Guide.