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Re: st: standard error of the odds ratio


From   katsiaryna ivanova <kivanova@usc.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: standard error of the odds ratio
Date   Wed, 28 Sep 2005 15:02:23 -0700

Thanks a lot, May. It is very helpful.

Best wishes, Kate

----- Original Message -----
From: May Boggess <mboggess@stata.com>
Date: Monday, September 26, 2005 2:45 pm
Subject: Re: st: standard error of the odds ratio

> On Monday morning Kate asked about the standard error of the odds 
> ratio:> 
> > I need to calculate the standard error of the odds ratio and use 
> the "cc"
> > command which reports the 95% confidence interval but does not 
> report the
> > standard error itself. I would appreciate it very much if anyone 
> could let
> > me know if there is a way or an option to specify that the 
> standard error of
> > the odds ratio be reported in the output as well.
> 
> The epitab command -cc- reports, by default, an exact confidence 
> interval for the odds ratio, so there is in fact no standard error 
> when 
> the interval is computed this way.
> 
> One thing Kate might want to do is to use the Woolf confidence 
> interval. 
> One can obtain the upper and lower bounds of the interval using 
> the 
> option -woolf- on -tabodds-. A standard error is reported if we 
> use the 
> command -logistic- to obtain the Woolf confidence interval. Here 
> is an 
> example that shows what I mean by all of this:
> 
>  clear
>  webuse downs
>  expand pop
>  cc case exposed
>  cc case exposed, wo
>  logistic case exposed
> 
> Now, you may notice that the interval is not symmetric so one 
> doesn't 
> just add and subtract 1.96*se to get the confidence interval. It 
> is in
> confidence interval of the log of the odds ratio that is symmteric.
> Here is how the above interval is calculated (I'm using the option 
> -coef- on -logistic- to show the actual coefficients of the model
> as opposed to the odds ratio here):
> 
>  logistic case exposed, coef
>  display "or = " exp(_b[exposed])        	
>  display "lb = " exp(_b[exposed]-invnorm(0.975)*_se[exposed])
>  display "ub = " exp(_b[exposed]+invnorm(0.975)*_se[exposed])
> 
> So what is the standard error that -logistic- reports then?  The 
> standard error of the odds ratio is
> 
>   display "se(OR) = " exp(_b[exposed])*_se[exposed]
> 
> (see [R] logistic, page 67 in version 9 manuals).
> 
> --May
> mmb@stata.com
> 
> 
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