What statement is used in SAS to keep the value of a calculated variable between observations?

The RETAIN statement in SAS is specifically designed to maintain the value of a variable from one observation to the next within a data step. By default, variables in a SAS dataset are initialized to missing at the start of each iteration of the data step. However, when the RETAIN statement is employed, it prevents the variable from being reset, allowing its value to persist across iterations. This is particularly useful when you need to hold onto a cumulative sum, a lagged value, or any calculated result that needs to be accessed across multiple rows of data.

For instance, if you're calculating a running total or need to reference a value from the previous observation, using the RETAIN statement ensures that the calculated variable retains its value rather than resetting to missing each time. This directly supports the need for continuity in data calculations over multiple records.

The other options serve different functions: the OUTPUT statement is used to write data to a new dataset or output a record, the DROP statement is utilized to exclude specified variables from the output dataset, and the KEEP statement is for including only certain variables in the output set. None of these other statements provide the functionality of retaining a variable's value through multiple observations.