Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
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 11:54:58 +0200 |
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. > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/statalist-faq/ > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/