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Jest
Obsidian | Level 7

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

2 REPLIES 2
PGStats
Opal | Level 21

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;
PG
mkeintz
PROC Star

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;
--------------------------
The hash OUTPUT method will overwrite a SAS data set, but not append. That can be costly. Consider voting for Add a HASH object method which would append a hash object to an existing SAS data set

Would enabling PROC SORT to simultaneously output multiple datasets be useful? Then vote for
Allow PROC SORT to output multiple datasets

--------------------------

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