Identify treatment discontinuation date

[riya275]

Hi ,

I have data that looks like - 

ID	Drug	Episode	start_date	end_date
1	A	1	1-Jan	30-Mar
1	A	2	1-May	3-Jul
1	A	3	28-Sep	28-Oct
1	A	4	1-Nov	30-Nov
1	B	1	1-Apr	10-May
1	B	2	2-Nov	28-Dec
1	C	1	1-Jul	2-Aug

data abc;
input ID $ drug $ episode start_date date9. end_date date9.;
format start_date end_date date9.;
informat start_date end_date date9.;
datalines ;
1 A 1 01Jan2012 30Mar2012
1 A 2 01May2012 03Jul2012
1 A 3 28Sep2012 28Oct2012
1 A 4 01Nov2012 30Dec2012
1 B 1 01Apr2012 10May2012
1 B 2 02Nov2012 28Dec2012
1 B 3 01Jan2012 30Mar2012
1 C 1 01Jul2012 02Aug2012
;
run;

Here we have subjects and the the drugs they take. A new episode of one drug means that the person discontinued. 

If the start date ( start date of 1st episode) of second drug consumed , lies in between the episodes of first drug , then we will ignore all the further episodes of 1st drug.

Eg. here 1 april ( start date of drug B) lies after the first episode of drug A, so episode 2,3,4 of drug A would be deleted.

Similarly the start date for drug C lies after the end date of episode 1 for drug B then episode 2 of drug B would be deleted. 

The maximum number of episodes a subject can have is 15.

The resultant dataset should look like - 

ID	Drug	Episode	start_date	end_date
1	A	1	1-Jan	30-Mar
1	B	1	1-Apr	10-May
1	C	1	1-Jul	2-Aug

[andreas_lds]

Can you please post what you expect as result? And please post data in usable form, especially the date-variables are important, because a date is not a date if the year is missing.

[Kurt_Bremser]

Please post example data in a WORKING data step with datalines, and make sure you have usable data. Dates without years are useless.

[Kurt_Bremser]

Shouldn't we have two observations for drug B as the last observation of B ends (30mar2012) before the start of C?

Anyway, this is what I come up with:

data abc;
input ID $ drug $ episode start_date :date9. end_date :date9.;
format start_date end_date date9.;
informat start_date end_date date9.;
datalines ;
1 A 1 01Jan2012 30Mar2012
1 A 2 01May2012 03Jul2012
1 A 3 28Sep2012 28Oct2012
1 A 4 01Nov2012 30Dec2012
1 B 1 01Apr2012 10May2012
1 B 2 02Nov2012 28Dec2012
1 B 3 01Jan2012 30Mar2012
1 C 1 01Jul2012 02Aug2012
;

data firsts (keep=id count start_date rename=(start_date=first_date));
set abc;
retain count;
by id drug;
if first.id then count = 0;
if first.drug;
count + 1;
run;

data want;
set abc;
by id drug;
retain count;
if _n_ = 1
then do;
  declare hash f (dataset:"firsts");
  f.definekey("id","count");
  f.definedata("first_date");
  f.definedone();
  call missing(first_date);
end;
if first.id then count = 1;
if first.drug then count + 1;
rc = f.find();
put id= drug= count= rc= start_date first_date;
if rc = 0 and start_date > first_date then delete;
run;