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st: clogit or logistic for matched pairs

From   Michael Ingre <>
To   <>
Subject   st: clogit or logistic for matched pairs
Date   Thu, 06 Nov 2003 17:01:18 +0100

Dear statalist

I want to estimate the risk for an exposed twin to develop a symptom
relative an unexposed twin. I have 169 pairs of monozygotic twins that are
discordant on my exposure variable. The basic design is a case (exposed) -
control (unexposed) study. The outcome variable (symptom) is binary coded.

The most obvious method should be -clogit- however, I'm not satisfied with
the statistics.

Like McNemar, it excludes the ties between cases and controls and the odds
ratio returned describes the ratio of cases "winning" over controls.
However, I would like to estimate the ratio of a case to HAVE the symptom
(not "winning") compared to the control.

I have been criticized for using logistic regression with the cluster option
and robust variance estimator. My OR is said to be invalid.

Actually, the criticism is harder than that: My analyses is said to be
"completely meaningless".

. logistic dv iv , cluster(twinpairid)

Do you have any advice?

Thanks in advance

Michael Ingre

Department of Psychology
Stockholm University &
National Institute for
Psychoscial Medicine

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