Hi, I am trying to create a time-varying covariate that indicates whether someone was taking drug 1 (drugcat=0), drug 2 (drugcat=1), or drug 1+ drug 2 (drugcat=2). I want to run a Cox proportional hazards regression (proc phreg) that incorporates the fact that the drugs people are taking changes over time. Here is a simplified version of the data I have:
|
ID
|
Drug1StartDate1
|
Drug1EndDate1
|
Drug1StartDate2
|
Drug1EndDate2
|
Drug2StartDate1
|
Drug2EndDate1
|
Drug2StartDate2
|
Drug2EndDate2
|
age
|
sex
|
censor
|
|
1
|
June 1 2011
|
July 1 2011
|
|
|
|
|
|
|
50
|
0
|
0
|
|
2
|
Jan 1 2012
|
Dec 31 2012
|
|
|
June 1 2012
|
Dec 31 2012
|
|
|
40
|
1
|
1
|
|
3
|
Jan 1 2010
|
June 15 2010
|
July 1 2010
|
Dec 1 2010
|
Feb 1 2010
|
June 30 2010
|
Sept 15 2010
|
Dec 15 2010
|
60
|
1
|
0
|
I want the start and stop times in days that they are in each drug category. It’s not so hard when someone falls into only one category (ID=1) or two categories (ID=2) but it gets really tricky when people move between the categories (ID=3 is on only drug 1 from Jan 1-Jan 31, then on both drugs from Feb 1 to June 15, then on only drug 2 from June 16-30, then back to drug 1 from July 1 to Sept 14, then on both drugs from Sept 15 to Dec 1, then only on Drug 2 from Dec 2 to Dec 15. Some people have up to 20 start/stop dates so I can't really muscle through each possible variation.
Here is what I'd like my data to look like:
|
ID
|
Start
|
Stop
|
Drugcat
|
age
|
sex
|
censor
|
|
1
|
0
|
30
|
0
|
50
|
0
|
0
|
|
2
|
0
|
152
|
0
|
40
|
1
|
0
|
|
2
|
152
|
365
|
2
|
40
|
1
|
1
|
|
3
|
0
|
31
|
0
|
60
|
1
|
0
|
|
3
|
31
|
167
|
2
|
60
|
1
|
0
|
|
3
|
167
|
182
|
1
|
60
|
1
|
0
|
|
3
|
182
|
257
|
0
|
60
|
1
|
0
|
|
3
|
257
|
334
|
2
|
60
|
1
|
0
|
|
3
|
334
|
365
|
1
|
60
|
1
|
0
|
Ultimately I’ll use this code to run my regression (where drugcat=0 means drug 1 alone, drugcat=1 means drug 2 alone and drugcat=3 means both drugs at the same time):
Proc phreg data=want;
Class drugcat;
Model (start, stop)*censor(0)=drugcat age sex/rl;
Run;
I’ve tried using arrays to get the data I want but it quickly falls apart when someone switches between the drug categories more than once.
Can anyone tell me a better way to get to my goal? Thanks in advance!
