Raoul-
If your frequency matching was successful the distribution of whatever
variable you matched on should be the same in your cases and controls.
(You can look at whether the matching was successful, of course, with a
simple tabulation by case status.) You don't need to use conditional
logistic regression, which uses the matched set as the base unit for
analysis and takes the loss of independence between observations imposed
by 1:n matching into effect - if you do use it, incorrectly, it will
decrease the power to detect associations and provide inappropriately
broad confidence intervals for your coefficient estimates.
If your frequency matching was incomplete you can include the match
variable in your analyses to control for it. Controlling for age by
frequency matching might still be inadequate if the variable
distribution within a subgroup is patterned in a fashion related to your
outcome and exposure, in which case you can control for it to some
extent by including it in your multivariate analysis. (For example, for
some women's health outcomes, even after frequency matching on age we
might still need to take age into account in the analysis because age
has a different effect in women before and after menopause and our
matching didn't correct for that.)
Hope that helps,
Jen Marino
University of Washington
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Raoul C
Reulen
Sent: Sunday, April 02, 2006 6:37 AM
To: [email protected]
Subject: st: frequency matching in case-control study
Hi,
If I would conduct a case-control study and would want to frequency
match cases and controls, what STATA command would I have to use? Can I
simply include a variable that presents the group id (1=males age 50,
2=males age 60, 3=female age 50 etc.) and use .logit? Or should I use
.clogit? My understanding is that the command .clogit is used for
individual matched case-control data. Thanks.
Raoul
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