Attempting to flag overlaps based on drug class

[cmccor]

Hi all,

I am having a really hard time attempting to flag users that are concurrently using two different classes of medications. My goal is to flag any dispensing of a drug if it overlaps with a drug of another class on the start of the dispensing.

I have created an example data set to show what I mean. So essentially I have:

Obs	User	Drug_Class	Year_Month	Start_date	End_Date
1	1	A	201101	01/01/2011	01/20/2011
2	1	A	201101	01/15/2011	02/15/2011
3	1	B	201102	02/01/2011	02/10/2011
4	1	A	201102	02/11/2011	02/20/2011
5	2	A	201101	01/05/2011	01/20/2011
6	2	B	201101	01/15/2011	02/15/2011
7	2	A	201101	01/12/2011	01/30/2011

Where class A and Class B are two different drug classes. I only care about when there is an overlap of use of a drug in Class A and Class B, not when there is an overlap of drug in the same class. So ultimately, I would want a new flag variable that would look like this:

Obs	User	Drug_Class	Year_Month	Start_date	End_Date	Flag
1	1	A	201101	01/01/2011	01/20/2011	0
2	1	A	201101	01/15/2011	02/15/2011	0
3	1	B	201102	02/01/2011	02/10/2011	1
4	1	A	201102	02/11/2011	02/20/2011	0
5	2	A	201101	01/05/2011	01/20/2011	0
6	2	B	201101	01/15/2011	02/15/2011	1
7	2	A	201101	01/12/2011	01/30/2011	1

So observation 2 doesn't get a flag because it's an overlap of a drug in the same class, but then on the dispensing in observation 3 would get a flag since it is a dispensing of a drug in class B while they were taking a drug of class A.

The "Year_Month" variable is only relevant because I want to know the month in which they started concurrent use of a drug in class A and B.

Any help would be greatly appreciated!

[Astounding · Accepted solution]

A reasonable (but untested, that's up to you) approach:

proc sort data=have;
   by user start_date;
run;

data want;
set have;
by user drug_class notsorted;
prior_end = lag(end_date);
if first.user=0 and first.drug_class=1 and start_date <= prior_end then flag=1;
else flag=0;
run;

In this case, I'm assuming that "same day" is an overlap.  If that's not the definition, then change "<=" to "<"

[PGStats]

This will flag all overlaps:

data have;
input User Drug_Class $ Year_Month $ (Start_date End_Date) (:mmddyy10.);
format start_date end_date yymmdd10.;
datalines;
1 A 201101 01/01/2011 01/20/2011
1 A 201101 01/15/2011 02/15/2011
1 B 201102 02/01/2011 02/10/2011
1 A 201102 02/11/2011 02/20/2011
2 A 201101 01/05/2011 01/20/2011
2 B 201101 01/15/2011 02/15/2011
2 A 201101 01/12/2011 01/30/2011
;

proc sql;
select 
	a.user,
	a.drug_class as class1,
	b.drug_class as class2,
	max(a.start_date, b.start_date) as overlap_start format=yymmdd10.,
	min(a.end_date, b.end_date) as overlap_end format=yymmdd10.,
	calculated overlap_end - calculated overlap_start + 1 as overlap_days
from 
	have as a inner join
	have as b on a.user=b.user and a.drug_class < b.drug_class and
		max(a.start_date, b.start_date) <= min(a.end_date, b.end_date);
quit;

User 	class1 	class2 	overlap_start 	overlap_end 	overlap_days
1 	A 	B 	2011-02-01 	2011-02-10 	10
2 	A 	B 	2011-01-15 	2011-01-20 	6
2 	A 	B 	2011-01-15 	2011-01-30 	16