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Re: st: bug in -xtile-
From
"Dr. Yu Chen" <[email protected]>
To
[email protected]
Subject
Re: st: bug in -xtile-
Date
Fri, 1 Feb 2013 09:02:00 -0600
Thank you Nick for the confirmation. I hope this issue will be
corrected in Stata 13.
On Fri, Feb 1, 2013 at 2:44 AM, Nick Cox <[email protected]> wrote:
>
> Now I agree with you. The code for -xtile- includes the test
>
> if `nquanti' > _N + 1 {
> di in red "nquantiles() must be less than or " /*
> */ "equal to number of observations plus one"
> exit 198
> }
>
> but a better test would be something like
>
> marksample touse
> qui count if `touse'
>
> if `nquanti' > r(N) + 1 {
>
> The total number of observations _N is not the right number to check
> against.
>
> Nick
>
> On Fri, Feb 1, 2013 at 3:21 AM, Dr. Yu Chen <[email protected]> wrote:
>
> > Nick, if this is -xtile- point of view, then it will not work if I
> > delete observations whose value<5000. See my code below.
> > In other words, in the first example I added an if condition, and in
> > the second example, I deleted those observations. Why is the result
> > different? I think this is an inconsistency in -xtile-.
> >
> > sysuse auto,clear
> > keep in 1/10
> > drop if price<5000
> > xtile decile=price , nq(10)
>
> > On Thu, Jan 31, 2013 at 8:08 PM, Nick Cox <[email protected]> wrote:
> >> In your example 6 values qualify as < 5000. -xtile- classifies into 10
> >> classes as best it can
> >>
> >> (Here -groups- is from SSC.)
> >>
> >> . groups price decile, sep(0)
> >>
> >> +----------------------------------+
> >> | price decile Freq. Percent |
> >> |----------------------------------|
> >> | 3,799 1 1 16.67 |
> >> | 4,082 2 1 16.67 |
> >> | 4,099 4 1 16.67 |
> >> | 4,453 6 1 16.67 |
> >> | 4,749 7 1 16.67 |
> >> | 4,816 9 1 16.67 |
> >> +----------------------------------+
> >>
> >> You seem to be saying that they should not be classified if there are
> >> less than 10. That's a point of view, but it is not -xtile-'s point of
> >> view.
> >>
> >> The values are of the new variable are not equally spaced integers,
> >> but they could not be given the request.
> >>
> >> Nick
> >>
> >> On Fri, Feb 1, 2013 at 1:45 AM, Dr. Yu Chen <[email protected]>
> >> wrote:
> >>> I think there is a bug in -xtile-. I ran the code below, and I still
> >>> got deciles, but they are incomplete. I would expect missing values
> >>> because there are not enough observations.
> >>> I use Stata 12.
> >>>
> >>> sysuse auto,clear
> >>> keep in 1/10
> >>> xtile decile=price if price<5000, nq(10)
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