In which type of data step would you typically use a BY statement?

Using a BY statement is most commonly associated with merging datasets in SAS. When you merge data sets, the BY statement specifies the key variable(s) that SAS should use to align the datasets correctly. This ensures that observations from each dataset are appropriately matched based on the values of the specified BY variables.

For instance, if you have two datasets that share a common variable—like ‘ID’—and you want to merge them based on that ID, you would sort both datasets by ID and then use a BY statement in the DATA step to perform the merge. When the datasets are aligned using the BY variable, SAS can correctly combine the corresponding observations, which is essential for accurate data analysis.

In contrast, creating a new variable typically does not require a BY statement, as it often involves simple operations on existing variables without regard to grouping. Sorting data is a prerequisite step that can be done using a SORT procedure before merging but does not involve a BY statement within the context of a DATA step. Summarizing data generally makes use of the PROC MEANS or PROC SUMMARY procedures, where the BY statement may apply but it differs from merging datasets as the primary intention here is not to combine but rather to aggregate the data.