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Re: st: Keep/Drop Observations for Top/Bottom X%


From   "Justina Fischer" <JAVFischer@gmx.de>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Keep/Drop Observations for Top/Bottom X%
Date   Thu, 11 Oct 2012 12:10:00 +0200

Hi Lisa,

yes, you can program a local to take on the values of the x% percentile, and work with that variable throughout your regressions.

I am sure Nick can provide you with a code (I do not have an example ready in the moment)

HTH


Justina
-------- Original-Nachricht --------
> Datum: Thu, 11 Oct 2012 20:59:11 +1100
> Von: Lisa Wang <lhwang0925@gmail.com>
> An: statalist@hsphsun2.harvard.edu
> Betreff: Re: st: Keep/Drop Observations for Top/Bottom X%

> Thank you everyone for your suggestions. But I was wondering is there
> a way to code it up such that I don't need to do -summa- or -_pctile-
> and then look at the output to determine what the cutoff values will
> be for the top/bottom X% before I do the next step?
> 
> Thank you again,
> Lisa
> 
> 
> On Thu, Oct 11, 2012 at 8:54 PM, Justina Fischer <JAVFischer@gmx.de>
> wrote:
> > Hi Nick,
> >
> > in principle you might be right.
> >
> > However, for reasons of practicability it is sometimes recommendable for
> subset analysis to simply upload the full data and drop a part rather than
> working with an 'if' restriction throughout all regressions.
> >
> > HTH
> >
> > Jusitna
> >
> >
> > -------- Original-Nachricht --------
> >> Datum: Thu, 11 Oct 2012 10:46:02 +0100
> >> Von: Nick Cox <njcoxstata@gmail.com>
> >> An: statalist@hsphsun2.harvard.edu
> >> Betreff: Re: st: Keep/Drop Observations for Top/Bottom X%
> >
> >> You need not -keep- or -drop- to do this; in fact -keep- or -drop-
> >> here is usually a bad idea.
> >>
> >> (Furthermore, regressions of this kind are often more problematic than
> >> they seem, but I'll let others expand on that if they wish.)
> >>
> >> For full flexibility here, skip -summarize- and go straight to
> -_pctile-.
> >>
> >> For example,
> >>
> >> . sysuse auto
> >> (1978 Automobile Data)
> >>
> >> . _pctile mpg, p(10 90)
> >>
> >> . ret li
> >>
> >> scalars:
> >>                  r(r1) =  14
> >>                  r(r2) =  29
> >>
> >> So you can follow up with
> >>
> >> ... if mpg >= 29
> >>
> >> Warnings:
> >>
> >> 1. Watch out for ties.
> >>
> >> 2. Watch out for missing values at the top end.
> >>
> >> ... if mpg >= 29
> >>
> >> would include missings on -mpg- (if there were any).  -if inrange(mpg,
> >> 29, .)- excludes the missings.
> >>
> >> Nick
> >>
> >> On Thu, Oct 11, 2012 at 10:34 AM, Lisa Wang <lhwang0925@gmail.com>
> wrote:
> >>
> >> > I am unsure as to how I would go about keeping or dropping the
> >> > top/bottom X% of observations of a variable. I would like to do this
> >> > for further analysis on a subset of my data. For instance, I want to
> >> > do some further regressions for the top 10% of my observations based
> >> > on 'distance from home' and not the whole data set.
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