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RE: st: Adjusted Prevalence from Logistic models


From   Abdelouahid Tajar <a_tajar@hotmail.co.uk>
To   statalist <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Adjusted Prevalence from Logistic models
Date   Wed, 24 Oct 2012 10:46:05 +0100

Hi,

You can use "margins, at"

webuse margex

logit outcome i.sex i.group,or

margins, at(sex==1 group==1)


OR, if you use xi

 xi: logit outcome sex i.group,or

margins, at(sex==1 _Igroup_2 ==0 _Igroup_3==0 )



BW,

Abdelouahid

> Date: Wed, 24 Oct 2012 03:18:11 -0500
> To: statalist@hsphsun2.harvard.edu; statalist@hsphsun2.harvard.edu
> From: richardwilliams.ndu@gmail.com
> Subject: Re: st: Adjusted Prevalence from Logistic models
> 
> At 01:18 AM 10/24/2012, Dean Eurich wrote:
> >Hi all,
> >
> >A simple question. If I run a logistic model:
> >
> >logistic BB age sex rural
> >
> >I get the OR for the effect of rural (which is a flag for rural=0 or 
> >urban=1 dwelling) on the use of beta blockers (medication used to 
> >treat cardiovascular disease).
> >
> >A reviewer has asked for us to present the adjusted prevalence for 
> >the use of BB by rural and urban status. I am not to sure how to do this.
> >
> >I assume I could use the 'margin' command.
> >
> >So would it be as simple as
> >
> >  margins rural, atmeans
> >
> >(Although I realize I could do it as specific levels of sex and age as well)
> >
> >Thanks
> >
> >Dean
> 
> I'm not totally sure how you want to adjust. But if you want to use 
> -margins- you should use factor variable notation, e.g.
> 
> logistic BB age i.sex i.rural
> margins rural, atmeans
> 
> In general, I am not crazy about the atmeans option, and I especially 
> don't like it when you have a variable like sex in the model. You'll 
> be plugging in something like .5 for sex (the average person is half 
> male, half female?) I'd rather use the default -asobserved- or plug 
> in specific values or ranges of values for the other variables. For 
> some highlights of what you can do with margins, see
> 
> http://www.nd.edu/~rwilliam/stats/Margins01.pdf
> 
> As a sidelight, when you say rural=0 or urban=1, that sort of sounds 
> to me like heads I win, tails you lose. Aren't rural=0 and urban=1 
> the same thing?
> 
> -------------------------------------------
> Richard Williams, Notre Dame Dept of Sociology
> OFFICE: (574)631-6668, (574)631-6463
> HOME:   (574)289-5227
> EMAIL:  Richard.A.Williams.5@ND.Edu
> WWW:    http://www.nd.edu/~rwilliam
> 
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