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st: panel data sorting

From   Kit Baum <>
Subject   st: panel data sorting
Date   Fri, 19 Aug 2005 06:43:56 -0400

Steve wrote
I have a large company data base in which I have the following
variables among others:  Company ID (ID), Age (age), Year (Year).

I have data from 1992-2002 and would like to keep a cohort of data for
companies that were started in 1994.  Therefore, I generated a new
variable that combines Age and Year (ageyear) to identify those
companies started in that year.  However,I cannot seem to devise a way
to keep data for those companies for subsequent years. Any help would
be appreciated!

webuse grunfeld,clear
gen int var7 = 1930 in 1
replace var7 = 1929 in 21
replace var7 = 1934 in 41
replace var7 = 1934 in 61
rename var7 yrstart
bysort company: egen start=mean(yrstart)
* I want only the histories of those companies started in 1934
keep if start==1934
tab company

Kit Baum, Boston College Economics

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