What is the correct form of the sum statement in a DATA step?

The choice stating that the correct form of the sum statement in a DATA step is "total + var1 + var2;" is accurate because it showcases a specific feature in SAS called the "automatic summation." When using this syntax, the variable total accumulates the sum of itself and the values of var1 and var2 as the DATA step iterates through each observation.

This formulation allows for a running total to be maintained throughout the DATA step processing. By simply using the plus sign with the variable names, SAS knows to retain the previous value of total and add the current values of var1 and var2 for each iteration of the DATA step.

Using "total = sum(var1, var2);" or "total = total + var1 + var2;" creates a new assignment for total. The former relies on the SUM function, which does not include the previous value of total as part of its calculation. The latter explicitly resets total in each iteration, which can lead to incorrect accumulation if accumulating values continuously.

Overall, the syntax you provided represents the simplest and most efficient way to maintain a running total during the DATA step processing in SAS.