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RE: st: RE: Imputed Missing Values with Uvis


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Imputed Missing Values with Uvis
Date   Thu, 24 Feb 2005 23:36:07 -0000

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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