What does the KEEP statement do in a DATA step?

The KEEP statement in a DATA step is used to specify which variables from the input dataset should be retained in the output dataset. By using the KEEP statement, you can limit the output to include only the variables you are interested in, which can help reduce the dataset's size and complexity.

When applied in a DATA step, the KEEP statement has a direct impact on the output dataset, allowing you to control the variables that are carried forward. This is particularly useful when working with large datasets that contain many variables, some of which may not be necessary for your analysis or reporting needs. By explicitly stating which variables to keep, you ensure that only relevant data is retained, enhancing both efficiency and clarity in subsequent data processing steps.

The other options do not reflect the functionality of the KEEP statement. Combining datasets, removing observations, or formatting output are outside the scope of what the KEEP statement accomplishes in a DATA step. Understanding the KEEP statement is essential for effective data manipulation within SAS programs.