What is the purpose of the BY statement in a PROC step?

The purpose of the BY statement in a PROC step is fundamentally to perform analyses on subgroups of data. When the BY statement is used, SAS processes the data in the order specified by the BY variables. This allows the procedure to create separate analyses for each subgroup defined by those BY variables.

For example, if you have a dataset with sales information and you use a BY statement with a variable such as "Region," SAS will execute the procedure for each region individually. This means that any statistics, summaries, or analyses computed would be specific to each region, allowing for a clear comparison and understanding of the data within those specific subgroups.

The other options describe different functionalities that are not the primary purpose of the BY statement. While the BY statement does influence the order of processing and can implicitly group data for summary statistics, its core function is geared towards enabling analyses that are specific to the defined subgroups. Thus, the primary reason for using the BY statement is to enhance the analytical capabilities over different categories within the dataset.