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st: Duplicate combinations of variables

From   Miranda Kim <>
Subject   st: Duplicate combinations of variables
Date   Thu, 25 Mar 2010 14:18:09 +0000

I am a Stata 11 user, and I wonder if anyone has advice on achieving the following: I have two variables, one with ID numbers for cases and one with ID numbers for matched controls in a case control study. There are 3 controls matched to each case, and a subject may serve as a control for more than one case or later become a case. I am wanting to check that in my dataset all the pairs of cases and their matched control are unique; ie that I don’t have for example:
Case ID Control ID
123 253
253 123
Any suggestions would be of great help!
Many thanks and best wishes,

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