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# RE: st: Interpolation using cipolate

 From "joe J." To statalist@hsphsun2.harvard.edu Subject RE: st: Interpolation using cipolate Date Wed, 14 Apr 2004 19:45:17 +0000

```Thanks Nick. I got the awakening when Richard gave the reply.

```
```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 19:12:26 +0100

-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.

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

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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