In a SUM function, which type of value is included in the result?

The SUM function in SAS is designed to calculate the total of a set of values while specifically excluding any missing values from the computation. This feature makes it particularly useful when dealing with datasets that may contain gaps or missing entries. When the function encounters a missing value, it simply disregards it in the summation process, ensuring that only valid numerical entries contribute to the final result. This approach helps to maintain the integrity of numerical analyses, allowing for more accurate and meaningful statistical outcomes.

The other options do not accurately describe the behavior of the SUM function; for instance, the inclusion of all values would lead to potentially misleading results in cases where data is incomplete, and accounting for future or only the first value is not relevant to the SUM function's intended operation.