Which method is used to concatenate datasets in SAS?

The method used to concatenate datasets in SAS is through the SET statement in a DATA step. When using the SET statement, multiple datasets can be combined into a single dataset by stacking them on top of one another. This is particularly useful when the datasets share the same structure, meaning they have the same variable names and types.

By incorporating the SET statement, all observations from each specified dataset are read in their entirety, and they are sequentially added to the final dataset. This allows for a straightforward concatenation of datasets where the order of the datasets in the SET statement determines the order of the observations in the resulting dataset.

The other methods mentioned serve different purposes. The MERGE statement is specifically designed for combining datasets based on common variables (i.e., merging), rather than concatenating them. The APPEND procedure allows for adding observations from one dataset to another, but it is fundamentally different from the concatenation performed by the SET statement as it involves a procedure rather than a straightforward DATA step. Likewise, the SQL UNION command is part of the SQL procedure in SAS and is typically used for combining datasets that might not necessarily be column-wise aligned, rather than for simple concatenation in a data manipulation context.