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Re: st: excluding single measurements in time
From
Nick Cox <[email protected]>
To
[email protected]
Subject
Re: st: excluding single measurements in time
Date
Wed, 27 Feb 2013 10:44:20 +0000
Assuming a -school- identifier and given a -syr- variable then it will
be diagnostic whenever only one year is represented for each school in
that case
bysort school (syr) : drop if syr[1] == syr[_N]
This is also an FAQ:
FAQ . . . . . . Listing observations in a group that differ on a variable
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox
11/01 How do I list observations in a group that differ
on a variable?
http://www.stata.com/support/faqs/data-management/listing-observations-in-group/
Don't be misled by the FAQ title. It does cover what I think is your
problem, except that you want to -drop-, not -list- and you want
values the same, which is covered in the FAQ.
Nick
On Wed, Feb 27, 2013 at 9:56 AM, John Singhammer <[email protected]> wrote:
> I am investigating growth in physical fitness among 58.000 children in
> 206 schools.
>
> Individual level data has been collected in 2009, 2010 and 2011.
> individuals are nested within classes, within schools.
> The schools volunteered to participate in the study and hence, data
> are unbalanced as can be seen from the output below.
>
> For a particular analysis, I want to select the schools (children
> within schools) with repeated measures. That is, I want to exclude
> schools with measurements at only a single point in time.
>
> How do I come about that in stata?
> . xtdescribe
>
> pnr: 137400, 347246, ..., 1.231e+10 n = 58041
> syr: 2009, 2010, ..., 2011 T = 3
> Delta(syr) = 1 unit
> Span(syr) = 3 periods
> (pnr*syr uniquely identifies each observation)
>
> Distribution of T_i: min 5% 25% 50% 75% 95% max
> 1 1 1 2 2 2 3
>
> Freq. Percent Cum. | Pattern
> ---------------------------+---------
> 27306 47.05 47.05 | .11
> 16079 27.70 74.75 | ..1
> 11318 19.50 94.25 | .1.
> 2109 3.63 97.88 | 111
> 597 1.03 98.91 | 1.1
> 346 0.60 99.51 | 1..
> 286 0.49 100.00 | 11.
> ---------------------------+---------
> 58041 100.00 | XXX
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