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Re: st: Pulling out observations based on a condition


From   Jeph Herrin <junk@spandrel.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Pulling out observations based on a condition
Date   Wed, 29 Jul 2009 11:00:17 -0400


By "pull out", do you mean "drop" or "keep"? Here's a way
to keep them. Let -id- identify individuals, -time-
identify periods, and -status- be dichtomous variable of
interest.

 /* tag those who transition from period to period */
 bys id (time) : gen transition=(status!=status[_n-1])|(_n==1)

 /* check if individual always transitions */
 bys id : egen alwaystransits=min(transition)

 /* if they always transitioned, notrans==0 */
 keep if alwaystransits

This keeps those who transition between every time period.

hth,
Jeph




Dmitriy Krichevskiy wrote:
Dear Statalisters,

I have a panel data set with about 14000 people and 21 time periods. I
wanted to pull out persons who have transitioned from one category of
the same dichotomous variable to another (say from lowest income
quintile to the highest) during one time increment - for the whole
duration on the sample. So, essentially, I need to pull out all the
people that did that transition from first period to second plus from
second to third and so on... I know it is a simple loop but whatever I
do Stata drops all of the observations. Perhaps, I should also mention
that I am new to programing altogether. Thanks for all of your help,
Statalisters definitely  will be thanked in my dissertation.
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