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st: RE: Creating a Count Variable in STATA


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Creating a Count Variable in STATA
Date   Sun, 3 Apr 2005 15:40:14 +0100

This question evoked a variety of correct 
and incorrect answers. The most satisfying 
solution from first principles is surely 

bysort ccode (year) : gen nukecount = sum(nukes) 

but with -tsset- data and -tsspell- from SSC 

tsspell nukes 

creates the variable required automatically 
as -_seq-. The other variables created by -tsspell- 
are probably no use here. 

Nick 
n.j.cox@durham.ac.uk 

Michael
 
> I have a time series dataset organized by country year, with 
> one entry per
> year per country.  I want to create a count variable that measures the
> number of years it has been since a given country has acquired nuclear
> weapons, the variable of interest for my study.  But I am 
> having trouble
> getting the coding entirely right.  The variables that I 
> "think" matter
> here are:
> 
> -ccode: the country code for each country
> -nukes: a binary variable that is 0 if a country does not have nuclear
> weapons and a 1 if it has nuclear weapons
> -year: this is pretty obvious. .
> 
> The current coding I have is:
> 
> gen nukecount=0
> replace nukecount=(nukecount[_n-1]+1) if ((ccode==ccode[_n-1]) &
> (nukes==1) & (nukes[_n-1]==1))
> 
> If anyone has some advice about what I am doing wrong and how to
> potentialy correct it. . that would be fantastic and I would really
> appreciate it.

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