topic Questions on matching controls to cases? in SAS Programming

Questions on matching controls to cases?

gizat — Fri, 19 Jun 2020 06:31:36 GMT

Dear SAS experts,

For my matched case-control study, I’m preparing my data for a conditional logistic regression. Using the matching variables, I’ve got a dataset containing the details for cohort (cases and controls identified). At this stage I know my cases and the controls. However, I do not know which controls were matched to which case. I need to make risk sets or strata so that I can perform conditional logistic regression.

Each case and control have unique identifying variable, I want to identify the controls matched to each case. Could you please help me how I can link the cases to their matched controls and assign them a specific id for each? My matching ration is 1:3.

Looking forward to hearing from you.

Thank you,

Re: Questions on matching controls to cases?

smantha — Fri, 19 Jun 2020 13:43:25 GMT

Do you know if the match variables overlap between cases. If not you can use the following logic. Group is the variable that has case or control values.
Proc sort data= have; by match1 match2 match3 group
Data want;
Set have;
By match1 match2 match3;
Retain caseno 0;
If first.match1 then caseno=caseno+1;
Run;
This works well only if match1 match2 and match3 are all discrete values and matches are exact. If you are doing a match on ranges you can split your have dataset into two datasets one containing all the records of cases only, and the other containing all records. Then do a sql join on both datasets.

Re: Questions on matching controls to cases?

gizat — Tue, 23 Jun 2020 00:03:50 GMT

Hi Smantha,

Yes, they do. I've three matching variables; age (+-2 years), gender (match same gender) and year of hospital admission (+-2 years). What I want is to choose three controls for per case among possible controls and want to identify the controls matched to each case.

More help is appreciated!

Kind regards,