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Re: st: -margins- vs -adjust-


From   Fred Wolfe <fwolfe@arthritis-research.org>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: -margins- vs -adjust-
Date   Thu, 5 Nov 2009 04:22:10 -0600

Jeff's post and explanation was very helpful. I have been struggling
with the manual on margins since Stata 11 came out. Sometime I think I
understand it it, sometimes not. Perhaps Jeff could clarify this
further for me.

The manual states:

A margin is a statistic based on a fitted model calculated over a
dataset in which some of or
all the covariates are fixed at values different from what they really
are. For instance, after a linear regression fit on males and females,
the marginal mean (margin of mean) for males is the predicted mean of
the dependent variable, where every observation is treated as if it
represents a male; thus those observations that in fact do represent
males are included, as well as those observations that represent
females. The marginal mean for female would be similarly obtained by
treating all observations as if they represented females.

A simple question, what does it mean (precisely) "...where every
observation is treated as if it represents a male <snip>  treating all
observations as if they represented females." What actually is done so
they are "treated as if?"

Thanks,

Fred

--
Fred Wolfe
National Data Bank for Rheumatic Diseases
Wichita, Kansas
NDB Office  +1 316 263 2125 Ext 0
Research Office +1 316 686 9195
fwolfe@arthritis-research.org

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