Hi,
How can I calculate differences between measurements for a variable in a longitudinal dataset. I want to create a change from time 1 variable for VAR. measurement for time 2 - time 1, time 3 - time 1, time 4 - time 1....time 1 is the baseline.
This is how my data looks:
ID time VAR
1 1 84
1 2 80
1 3 75
1 4 85
2 1 86
2 2 80
2 3 77
2 4 74
Thanks
Use a retain statement to remember the baseline:
data want;
set have; by id;
retain baseline;
if first.id then baseline = var;
change = var - baseline;
drop baseline;
run;
proc print; run;
This is also a good problem to illustrate the benefits of a well-designed self-merge statement:
data want;
merge have (where=(time=1) rename=(var=baseline))
have;
by id;
change = var - baseline;
drop baseline;
run;
Are you ready for the spotlight? We're accepting content ideas for SAS Innovate 2025 to be held May 6-9 in Orlando, FL. The call is open until September 25. Read more here about why you should contribute and what is in it for you!
Learn how use the CAT functions in SAS to join values from multiple variables into a single value.
Find more tutorials on the SAS Users YouTube channel.