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;
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