Re: st: Panel data: how to deal with varbles existing in 98 but notin 99

[Rose Medeiros <rosem@cisunix.unh.edu>]

To me at least, the author seems to mean "variables" rather than 
"observations." Since she states that questions were asked at one wave, 
but not at the others. Her example, religion, is often presumed to be 
time invariant (i.e. people don't change their religions often), so it 
would make sense that it would only be asked at one point. It might be 
useful to know whether the "problem" variables are all of this sort or not.
Rose

Nick Cox wrote:


> This answer takes Nirina to mean "observations"
> when she says "variables". I did wonder this 
> myself, but it is not what she said. 
> Nick 
> n.j.cox@durham.ac.uk 
> Stas Kolenikov
>
>  
>
> > Depends on what you want to do with them. You can -drop- them, or you
> > can fill them in by
> >
> > sort panelid time
> > unab allvars : *
> > foreach x in varlist `allvars' {
> >   bysort panelid (time): replace x=x[_n-1] if mi(x)
> > }
> > This may lead to some awkward results, and sometimes the missing value
> > is a valid one (e.g. a wage of somebody who was employed in the first
> > period, but not in the second one), so if you know the variables you
> > want to fill in by the prior values, you should put them as the
> > varlist in -foreach- above.
> >    
> Nirina M. 
>  
>
> > > my question should be very easy but forgive my
> > > d..ness.
> > > I am creating a panel data but the trouble now is that
> > > there are variables that exist in the start of the
> > > survey but does not exist in the following year:(or
> > > sometimes new questions come up in the following year
> > > but were not asked before): say the religion, they ask
> > > it in 98 but not later.
> > >      
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