RE: st: Interpolation using cipolate

["joe J." <otharain@hotmail.com>]

I very much appreciate your response as it makes me doubly sure that what I 
understood  about -cipolate- is correct (given that you authored the 
programme). I already had a trial run and find it extremely suited for the 
job in hand. I am sorry that I did not mention that it is a user-written 
programme. Shall be careful next time.

Joe



> From: "Nick Cox" <n.j.cox@durham.ac.uk>
> Reply-To: statalist@hsphsun2.harvard.edu
> To: <statalist@hsphsun2.harvard.edu>
> Subject: RE: st: Interpolation using cipolate
> Date: Wed, 14 Apr 2004 21:06:35 +0100
>
> Good. But others might appreciate
> the explanation of what -cipolate-
> is. Among other advice, the Statalist
> FAQ suggests
>
> Say what command(s) you are using. If they are not part of
> official Stata, say where they come from: the STB/SJ, SSC,
> or other archives.
>
> Nick
> n.j.cox@durham.ac.uk
>
> joe J.
>
> > Thanks Nick. I got the awakening when Richard gave the reply.
> >
> > >-cipolate- is a user-written command on SSC for cubic
> > >interpolation. As Richard surmises, the logic is that
> > >you must interpolate gaps in a response with respect
> > >to a second variable (e.g. time), just as with official
> > >Stata's -ipolate-, which is for linear interpolation.
> > >
> > >Richard Williams replied to Joe J.
> > >
> > > > >A naive question. I just insalled cipolate to fill missing
> > > > values for one
> > > > >variable. The documentation tells me that interpolation is
> > > > done using two
> > > > >points before and two points after the missing value. That
> > > > said, why is it
> > > > >that the procedure requires a second variable? In other
> > words, for
> > > > >replacing missing values in variable y, why we need to
> > > > include variable x
> > > > >in the command?
> > > > >
> > > > >. cipolate y x, gen(yprime).
> > >
> > > > I don't know about -cipolate-, but the docs for -ipolate-
> > > > (reference manual
> > > > G-M, pp. 182-183) say that Y is a function of X.  The value for
> > > > interpolated Y is computed using values from the surrounding
> > > > Xs and Ys that
> > > > are not missing.
> > > >
> > > > If you are going to interpolate, your data have to be sorted
> > > > in some way,
> > > > right?  So having an X accomplishes that.  The distance
> > > > between Xs will be
> > > > related to the interpolated differences between Ys.
>
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