Change from Baseline Calculation : Clinical SAS

Change-from-Baseline:
The purpose of using change-from-baseline analysis data sets is to measure what effect some therapeutic intervention had on some kind of diagnostic measure. A measure is taken before and after therapy, and a difference and sometimes a percentage difference are calculated for each post-baseline measure. These data sets are generally normalized vertical structure data sets. Here is an example of how such a data set could be created for systolic and diastolic blood pressure data.

data bp;
input subject $ week test $ value;
datalines;
101 0 DBP 160
101 0 SBP 90
101 1 DBP 140
101 1 SBP 87
101 2 DBP 130
101 2 SBP 85
101 3 DBP 120
101 3 SBP 80
202 0 DBP 141
202 0 SBP 75
202 1 DBP 161
202 1 SBP 80
202 2 DBP 171
202 2 SBP 85
202 3 DBP 181
202 3 SBP 90
;
run;

**** SORT DATA BY SUBJECT, TEST NAME, AND WEEK;
proc sort data = bp;
by subject test week;
run;
**** CALCULATE CHANGE FROM BASELINE SBP AND DBP VALUES.;
data bp;
set bp;
by subject test week;
**** CARRY FORWARD BASELINE RESULTS.;
retain baseline;
if first.test then baseline = .;
**** DETERMINE BASELINE OR CALCULATE CHANGES.;
if visit = 0 then baseline = value;
else if visit > 0 then
do;
change = value – baseline;
pct_chg = ((value – baseline) /baseline )*100;
end;
run;

Advertisements

Tagged: ,

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: