topic Matching cases to controls without replacement in SAS Programming

Matching cases to controls without replacement

momolito — Thu, 04 May 2023 12:30:20 GMT

Hello

I am trying to match cases to controls randomly in a ratio of 1:5 by sex and age. I have a data set (HAVE - created by PROC SQL step) containing the cases and potential controls, with the variables below; (rand_num - assigned random numbers)

case_id, control_id, case_age, control_age, case_sex, control_sex, rand_num

I initially used the code below to select 5 controls for each case.

proc sort data=HAVE ;
by case_id rand_num;
run;

data WANT not_enough;
set HAVE;
by case_id ;
retain num;
if first.case_id then num=1;
if num le 5 then do;
output WANT;
num=num+1;
end;
if last.case_id then do;
if num le 5 then output not_enough;
end;
run;

How can I modify this in order to select 5 controls for each case without replacement (using controls only once)?

Thanks

Re: Matching cases to controls without replacement

rudfaden — Thu, 04 May 2023 12:51:55 GMT

Try to look at proc SURVEYSELECT

Re: Matching cases to controls without replacement

momolito — Sat, 06 May 2023 04:42:04 GMT

I have tried to use Proc surveyselect as you suggested with the code below. note - at this point I have 2 dataset, one for CONTROLS (n=>10000) and another for CASES (n=986). each contains the id, age and sex. I am trying to match in a ratio of 1:5 without repeating controls.

proc surveyselect data=CONTROLS method=srs out=matched_controls seed=12345 noprint samprate=5;
strata AGE SEX;
id ID;
run;

proc sql;
create table matched_pair as
select a.ID as case_id, b.ID as control_id
from cases a, matched_controls b
where a.age between b.age-5 and b.age+5
and a.sex = b.sex
and row_number()OVER(partition by a.Release_No)as <= 5;
quit;

However, my outcome still has duplicate controls and is not matching at the 1:5 ratio. How can i modify this to achieve what i want? I am quite new to SAS. Thanks in advance

Re: Matching cases to controls without replacement

Patrick — Sat, 06 May 2023 05:11:12 GMT

" I have a data set (HAVE - created by PROC SQL step) containing the cases and potential controls"

Please share your have data.

Re: Matching cases to controls without replacement

momolito — Sat, 06 May 2023 08:07:46 GMT

Hello Patrick

I have attached my 'Have' dataset (from the SQL step), as well as the cases and controls datasets.

Thanks for the help.