Statistical Analysis System (SAS) Programming Certification Practice Exam

How does SAS determine the FIRST.variable in a BY group?

1. It sets the value of FIRST.variable to 1 for the last observation in a BY group.

2. It sets the value of FIRST.variable to 1 when an observation is the first in a BY group.

3. It assigns a value of 0 for all observations in the BY group.

4. It sets the value of FIRST.variable to 0 for the first observation in a BY group.

The correct answer is: It sets the value of FIRST.variable to 1 when an observation is the first in a BY group.

The value of FIRST.variable is set to 1 when an observation represents the first record in a BY group during data processing in SAS. This is part of the automatic variable functionality in SAS, which has been designed to facilitate data manipulation when working with BY groups. When a dataset is sorted by one or more variables and then processed in a DATA step with a BY statement, SAS creates special variables that indicate the first and last observation in each group defined by the BY statement. When SAS encounters the first observation in each BY group, it automatically assigns a value of 1 to the FIRST.variable, allowing users to easily identify this position in various analyses and transformations. This is particularly useful in scenarios like cumulative calculations, generating reports, or other data summarization tasks where the identification of group boundaries is crucial. The other options do not accurately reflect this mechanism. The FIRST.variable indicates the start of a group, not the end or a constant value for all observations. Thus, the correct interpretation of how the FIRST.variable works aligns with the explanation provided in the selected response.