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st: Re: Marking/deleting subsets of observations related to some condition on that subset


From   "Michael Blasnik" <michael.blasnik@verizon.net>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: Marking/deleting subsets of observations related to some condition on that subset
Date   Tue, 9 Nov 2004 12:01:56 -0500

bysort person_id: egen interview_count=sum(question1!=-5)

should work.

Michael Blasnik
michael.blasnik@verizon.net

----- Original Message ----- From: "Jay McCarthy" <jay.mccarthy@gmail.com>
To: <statalist@hsphsun2.harvard.edu>
Sent: Tuesday, November 09, 2004 11:28 AM
Subject: st: Marking/deleting subsets of observations related to some condition on that subset



Dear STATALIST,

I have observation data for a survey. The survey has been conducted 10
times with some of the same people. Each person has an id that is used
each time. I would like to delete all observations related to people
who have not participated 6 or more times.

My strategy has been to first create a new variable that will be equal
to the number of interviews that person has had total. So, the 1998
data for person 1 will be "6" if they've been in 6 surveys and so will
the 2000 data.

I first tried,
"by person__id : egen interview__count = count( person__id ==
person__id & question1 != -5 "

The strategy here is that "question1" will be "-5" if the person was
not interviewed.

Then I tried...

forvalues pid = 1(1)12686 {
egen interview__count = count( person__id == `pid' & question1 != -5 )
if person__id == `pid'
}

The first failed for unknown reasons and the second succeeded for
"pid=1" but then failed for further runs because the variable already
existed. I would have used "replace" instead but the "count" function
is not available with replace.

My next try will be to use the above format to create
"interview__count$i" for each person, then run replace to set each
person's "interview_count" to "interview_count$i" but I think this is
poor way to do it and I'm looking for suggestions.

Thank you,
Jay McCarthy

--
Jay McCarthy <jay.mccarthy@gmail.com>
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