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Re: st: Discrete time hazard model - Interval width


From   gideluca@unical.it
To   statalist@hsphsun2.harvard.edu, Steve Samuels <sjsamuels@gmail.com>
Subject   Re: st: Discrete time hazard model - Interval width
Date   Wed, 19 May 2010 21:15:01 +0200

Dear Steve,
Thank you for your help.
The stock-sample includes all 2004 graduates at risk of finding a job (more precisely searching for a job and not pursuing other studies) who have been interviewed one year (2005), three years (2007) and five years (2009) after their graduation. So, we initially select only those who in the baseline interview 2004 are looking for a job. These individuals can remain in their unemployment state, find a permanent job or be lost to follow-up.

We do not know exactly the date of the first real job they find, we just know if at the time of each subsequent interview they have a stable job or not. In particular, the relevant questions to identify failures are: ?Are you working at this moment? and ?Is your job stable??. Graduates finding a stable job, say, in the first interview are our failures. So, they are not at risk anymore and they are discarded from the analysis. In addition, for people who had never gotten a "real job", the last observed interview serves to define our censoring points.

What?s wrong with ignoring in a discrete time hazard model the fact that interviews are not administered regularly over time?


Def. Quota Steve Samuels <sjsamuels@gmail.com>:

-
Giuliana-

You can use intervals of unequal lengths for a discrete or, in your
case, grouped, survival analysis. But exactly what information on job
history was obtained at each interview?

If you obtained  more specific information the date of the first real
job,  use that information to define your time variable.  For people
who had never gotten a "real job",  the  last observed interview will
serve to define censoring points.

Stephen Jenkins has some excellent resources about survival analysis.
http://www.iser.essex.ac.uk/study/resources/module-ec968
including his Lecture notes:
http://www.iser.essex.ac.uk/files/teaching/stephenj/ec968/pdfs/ec968lnotesv6.pdf

Steve

On Tue, May 18, 2010 at 8:51 AM,  <gideluca@unical.it> wrote:
Dear Stata Users,

We are assessing the transition from university to the first real job,
taking into account individual characteristics and the family background. We
use survey data including graduates from the summer sessions in the year
2004 who were interviewed at one, three and five years from graduation.  In
order to carry out the analysis we estimate a discrete time hazard model. We
have organised the data in such a way that for each student there are as
many data rows as there are time intervals over which the student is at risk
of finding the first job. Is it correct to use intervals of different width
(0-1; 1-3; 3-5)  given that we do not have yearly interviews?



       +-----------------------+
       id   studytim   dead
       -----------------------
279.    182          2      0
280.    182          2      1
281.    183          3      0
282.    183          3      0
283.    183          3      1
       -----------------------
284.    184          1      1
285.    185          3      0
286.    185          3      0
287.    185          3      1
288.    186          3      0
       -----------------------
289.    186          3      0
290.    186          3      0
       +-----------------------+

Thank you very much.
Giuliana

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Steven Samuels
sjsamuels@gmail.com
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USA
Voice: 845-246-0774
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