What does the SUM statement do in a DATA step?

The SUM statement in a DATA step is designed to accumulate a total across specified observations. When you use the SUM statement, it creates a running total by adding the values of specified variables cumulatively. This allows you to keep a continuous sum as you process each observation in your dataset, rather than calculating the sum only at the end of the DATA step. Consequently, with each new observation, the current total is updated, reflecting the addition of the value from the latest observation.

This functionality is particularly useful in scenarios where it is necessary to track cumulative totals, such as financial analysis, inventory management, and any situation where progress over time needs to be monitored. The SUM statement effectively allows for progressive calculations, maintaining an ongoing total without requiring a separate accumulation step for each observation.

In contrast, other answer choices describe different functionalities that do not align with what the SUM statement accomplishes. The statement does not average values, initialize variables, or reset totals for each observation, as those actions pertain to other processes within SAS programming.