The ANOVA Procedure
BY variables ;
You can specify a BY statement in PROC ANOVA to obtain separate analyses of observations in groups that are defined by the BY variables. When a BY statement appears, PROC ANOVA expects the input data set to be sorted in order of the BY variables. If you specify more than one BY statement, only the last one specified is used.
If your input data set is not sorted in ascending order, use one of the following alternatives:
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Sort the data by using the SORT procedure and a similar BY statement.
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Specify the NOTSORTED or DESCENDING option in the BY statement for the ANOVA procedure. 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.
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Create an index on the BY variables by using the DATASETS procedure (in Base SAS software).
Since sorting the data changes the order in which PROC ANOVA reads observations, the sort order for the levels of the classification variables might be affected if you have also specified the ORDER=DATA option in the PROC ANOVA statement.
If the BY statement is used, it must appear before the first RUN statement, or it is ignored. When you use a BY statement, the interactive features of PROC ANOVA are disabled.
When both a BY and an ABSORB statement are used, observations must be sorted first by the variables in the BY statement, and then by the variables in the ABSORB statement.
For more information about BY-group processing, see SAS Language Reference: Concepts. For more information about the DATASETS procedure, see Base SAS Procedures Guide.