differences between measurement longitudinal data

[Jest]

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

[PGStats]

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;

[mkeintz]

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;