topic cumulative exposure cox in SAS Programming

cumulative exposure cox

lillymaginta — Wed, 05 Sep 2018 12:18:51 GMT

I have the following data

id rx_start rx_end event event_date

1 1/1/2005 3/1/2005 1 2/1/2005

2 2/2/2005 4/3/2006 1 7/5/2005

3 4/4/2005 5/5/2005 0

data have;
informat rx_start rx_end event_date mmddyy10.;
format rx_start rx_end event_date date9.;
input id rx_start rx_end event  event_date;
cards;
1  1/1/2005 3/1/2005  1           2/1/2005
2  2/2/2005  4/3/2006  1           7/5/2005
3  4/4/2005  5/5/2005  0;
Run;

I want to create cumulative exposure intervals as the following

interval 1 ) time between rx_start and rx_end <30 days then interval=1 and event1=1 (code the event as 1 if occurred within this interval)

2) 1 month- 3months

3) 3-6 months

4) > 6 months

The same id can have multiple intervals and the event should be assigned to the interval where it happens

for example for id 2:

id interval start_date end_date event1

2 1 2/2/2005 03/03/2005 0

2 2 03/03/2005 05/02/2005 0

2 3 05/02/2005 07/31/2005 1

I want to fit this as a cox model

Re: cumulative exposure cox

RW9 — Wed, 05 Sep 2018 10:34:53 GMT

Please post test data in the form of a datastep!! we are not here to type test data in or guess what structure you have.

Should be pretty easy to do something like (not tested as not typing test data in!):

data want (keep=id interval_:);
  set have;
  interval=1;
  interval_start_date=rx_start;
  interval_end_date=intnx('days',rx_start,30);
  event1=ifn(interval_start_date <= event_date <= interval_end_date,1,0);
  output;
  interval=2;
  interval_start_date=intnx('months',rx_start,3);
  interval_end_date=intnx('months',rx_start,6);
  event1=ifn(interval_start_date <= event_date <= interval_end_date,1,0);
  output;
  interval=3;
  interval_start_date=intnx('months',rx_start,6);
  interval_end_date=intnx('months',rx_start,12);  /* Not sure what upper limit is? */
  event1=ifn(interval_start_date <= event_date <= interval_end_date,1,0);
  output;
run;

Re: cumulative exposure cox

lillymaginta — Wed, 05 Sep 2018 12:20:18 GMT

Thank you RW9 and apologize for not posting in a datastep format. Would it be possible to add a column to the code that indicates the interval (e.g. 1,2,3).

Thanks!

Re: cumulative exposure cox

RW9 — Wed, 05 Sep 2018 12:28:22 GMT

I did, its called Interval. Hope that is what you require?

Re: cumulative exposure cox

lillymaginta — Wed, 05 Sep 2018 13:06:07 GMT

Thank you for the prompt reply. The code generates the interval_start_date and interval_end_Date only but I need the additional variable that indicates the interval category to use it in the regession.