When using a BY statement in a DATA step, SAS creates two temporary variables for each BY variable:
FIRST.variable and LAST.variable. These are used to indicate the beginning and end of each BY group.
For Ellen's observation:
* First.State=1 because this is the first occurrence of the state "OH" in the dataset when sorted by the state variable, which makes it the beginning of a new group for "OH".
* Last.State=0 because Ellen is not the last observation
for the state "OH" group. In the given dataset snippet, there appears to be only one observation for the state
"OH", but since the data is sorted by state, and we don't see another "OH" below Ellen, we can deduce that Ellen's observation is not the last "OH" observation in the entire dataset. If there were no more "OH" observations following Ellen's, then Last.State would be 1.
The FIRST.variable is set to 1 for the first observation in each BY group and 0 for all other observations in the group. Conversely, LAST.variable is set to 1 for the last observation in each BY group and 0 otherwise. Since we're assuming that the dataset is larger than the snippet shown, and the data continues beyond what is visible, we must assume there are more observations for "OH" unless indicated otherwise.
References
* "SAS 9.4 Language Reference: Concepts." SAS Institute Inc.
* "BY-Group Processing" in "SAS Programming 1: Essentials" course material, SAS Institute.