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st: RE: Data Management


From   "Matt Spittal" <Matt.Spittal@cancervic.org.au>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Data Management
Date   Tue, 18 Nov 2008 14:04:48 +1100

Dear Raphael,

One way of approaching this is to use a combination of the -bysort- command and the explicit subscripting commands. For instance:

	bysort id: gen nzero = 1 if  count[_n - 2] == 0 & count[_n - 1] == 0 & count == 0

should identify the observations where there are three consecutive zeros for each person. (If it isn't quite what you want, a variation on this will do the trick.) Then

	drop if nzero == 1

will exclude these observations from the dataset. Alternatively, something like 

	xtpoisson count if nzero != 1

(or whatever commands you are using) will keep all the observations in the dataset, but exclude them from the analysis.  A very good description of subscripting within groups is given in the User's Guide in section 13.7.2, for Stata version 10.

Matt

matt.spittal@cancervic.org.au 



-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Raphael Fraser
Sent: Tuesday, 18 November 2008 1:26 PM
To: statalist@hsphsun2.harvard.edu
Subject: st: Data Management


I have longitudinal data with "id" as unique identifier, "timevar" as
the time variable and an outcome variable I call "count." The timevar
contains the elapsed time in minutes. I would like to exclude all
zeros where there are 3 or more consecutive zeros for each person. Can
anyone help?

id  timevar count
1    1         56
1    2         2
1    3         0
1    4         0
1    5         0
1    6         0
1    7         5
1    8         0
1    9         0
2    1         230
2    2         0
2    3         0
2    4        19

Raphael
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