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Re: st: RE: Imputed Missing Values with Uvis


From   Quang Nguyen <quangn@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: Imputed Missing Values with Uvis
Date   Thu, 24 Feb 2005 14:10:52 -1000

Dear Nick and Richard,

Thanks so much for your advices. I highly appreciate it. Yes I do
understand that we need to impute "y" ONLY for observations with
missing values. Uvis, however, imputes "y" for all observations. As a
result, the imputed "y" might has missing value if any of "x" is
missing on a given observation. Thanks Richard for offering an
execellent way of dealing with this interesting issue.

I truly enjoy this forum where any of my question is answered just
moments after it posted. You are GREAT!
Have A Wonderful Day!
All the best,

Quang  
  


On Thu, 24 Feb 2005 23:36:07 -0000, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> No doubt this is what is often
> wanted. But the help for -uvis-
> is explicit:
> 
> Note that uvis will not impute observations for which
> a value of a variable in xvarlist is
> missing. Only complete cases within xvarlist are used.
> 
> Nick
> n.j.cox@durham.ac.uk
> 
> Richard Williams
> 
> > At 10:03 PM 2/24/2005 +0000, you wrote:
> > >You seem surprised at this.
> > >
> > >If you don't know -x1-, you cannot
> > >predict -y- from -x1 x2 x3-; and
> > >so on.
> > >
> > >If you do know -y- you don't need
> > >to impute it.
> >
> > If I understand Quang correctly, then the latter is exactly
> > the point.
> > -uvis- should have just plugged in the observed value for y
> > rather than
> > even try to impute it; but instead, it plugged in a missing
> > value since one
> > or more of the Xs for that case was missing.
> >
> > I tried -uvis- on a data set where y was not missing but some
> > values of x
> > were.  The generated y had missing data whereas the original
> > y did not.
> >
> > I'm not that familiar with the programs but if nothing else
> > one work around
> > might be
> >
> > replace uvis_y = max(original_y, uvis_y)
> >
> > where uvis_y is the var generated by uvis. If I've done this
> > correctly,
> > then whenever -uvis- generated an unnecessary MD code for y,
> > the original
> > non-missing value for y will get plugged back in.
> 
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