In SAS, what does the SET statement do?

The SET statement in SAS is specifically designed to read an existing data set into the DATA step. This functionality allows SAS to access and utilize the data from that set for processing. By using the SET statement, you can pull in all the observations from the specified data set, which can then be manipulated or analyzed further within the DATA step.

This capability is essential when you need to perform operations such as data transformations, creating new variables, or applying conditional logic to the data. The data is read into the program data vector (PDV), where you can work with it before potentially writing results to a new data set.

The other choices do not accurately reflect the primary function of the SET statement. For instance, the option regarding updating existing data values does not capture the primary role of just reading the data; instead, you would use different statements for updating. Similarly, while merging data sets is a task often performed in SAS, it is typically accomplished using the MERGE statement rather than the SET statement. Lastly, creating a backup copy of the data is not a function of the SET statement but would involve different techniques, such as using the DATA step to copy data to a new data set.