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RE: st: RE: RE: CIs for the ratio of two adjusted predictions after logistic?


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: RE: CIs for the ratio of two adjusted predictions after logistic?
Date   Wed, 1 Aug 2007 17:34:37 +0100

Got it. 

Nick 
n.j.cox@durham.ac.uk 

Maarten buis
 
> --- Nick Cox <n.j.cox@durham.ac.uk> wrote:
> > I think in this the term 
> > 
> > _b[foreign] 
> > 
> > should be
> > 
> > _b[foreign] * foreign 
> > 
> > and that 
> > 
> > _b[foreignXmpg] * mpg
> > 
> > should be 
> > 
> > _b[foreignXmpg] * foreignXmpg
> 
> No, I am comparing for each value of mpg the predicted probability of
> foreign cars with the predicted probabilities of domestic cars. To do
> so I create a local `xb_for' which contains the linear predictor
> assuming the car is foreign and a local `xb_dom' which contains the
> linear predictor assuming that the car is domestic. (actually the
> locals contain the commands that will create the linear 
> predictors, but
> that is a detail) Consider the code for the linear predictor assuming
> that the cars are foreign. 
> 
> #delim ;
> local xb_for "_b[_cons] + _b[foreign] +
>               _b[mpg]*mpg + _b[foreignXmpg]*mpg" ;
> #delim cr
> In that case we know that the the variable foreign has value 1, so 
> 
> _b[foreign]*foreign = 
> _b[foreign]*1 = 
> _b[foreign]
> 
> similarly:
> 
> _b[foreignXmpg]*foreign*mpg = 
> _b[foreignXmpg]*1*mpg = 
> _b[foreignXmpg]*mpg
> 

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