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The SURVEYMEANS Procedure |

**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. For more information on estimating the variance of subpopulation means and totals from sample survey data, refer to Cochran (1977). However, note that you can produce a domain analysis with PROC SURVEYREG (see Example 62.7).

When a BY statement
appears, the procedure expects the input data sets to be
sorted in 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 using the SORT procedure with a similar BY statement.
- Use the BY statement options NOTSORTED or DESCENDING in the BY statement. 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 on the BY variables using the DATASETS procedure.

For more information on the BY statement, refer to the
discussion in *SAS Language Reference: Concepts*.
For more information on the DATASETS
procedure, refer to the discussion in the *SAS
Procedures Guide*.

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