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st: origin and enter in stcox


From   "Douglas Thomas" <Thomas@mgt.unm.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: origin and enter in stcox
Date   Mon, 24 Nov 2003 09:20:27 -0700

> I have a question about "origin" and "enter" in stset using Stata 8.0. I am studing firms and their expansion into foreign markets. The firms are under observation from Jan 1 1991 to Dec 31, 2000. However, they are at risk of foreign expansion from their inception (when the firm was founded). I set up the data using the following command
> stset edate, id(unique) failure(enter) enter(time entdate) origin(time foundy2) exit(time .)
> Origin is the variable foundy2 which is an integer of the firm's founding date. 
> Enter is a variable that records the date Jan 1, 1991 for every observation, because this is the date when the firms became under observation. I believe that this is the correct syntax. However for some reason when I check the _t0 and _t dates and when I use stdes, the firms are not calculated as being at risk from their founding date. In fact some of the firms were founded in 1848 so their time at risk should be much higher.
> Below is an example of the output from stedes. Note the earliest time at risk is 3403 and the max is 3653. Can anybody possibly help me with this. I would appreciate any help.
> 	failure _d:  enter
>    analysis time _t:  (edate-origin)
>              origin:  time foundy2
>   enter on or after:  time entdate
>   exit on or before:  time .
>                  id:  unique
> 
>                                    |-------------- per subject --------------|
> Category                   total        mean         min     median        max
> ------------------------------------------------------------------------------
> no. of subjects             2060   
> no. of records             20671    10.03447          10         10         19
> 
> (first) entry time                  17297.77        1096      16071      52595
> (final) exit time                   20950.77        4749      19724      56248
> 
> subjects with gap              1   
> time on gap if gap           250         250         250        250        250
> time at risk             7524930    3652.879        3403       3653       3653
> 
> failures                      71     .034466           0          0          9
> ------------------------------------------------------------------------------
>  
> 
> Thanks,
> 
> Doug Thomas
> 
> Anderson Schools of Management
> University of New Mexico
> MSC05 3090
> 1924 Las Lomas NE
> Albuquerque NM 87131-0001
> Phone: (505) 277-8892
> Fax: (505) 277-7108
> thomas@mgt.unm.edu
> http://www.unm.edu/~thomasd
> 
> 
> Thanks,
> 
> Doug Thomas
> 
> Anderson Schools of Management
> University of New Mexico
> MSC05 3090
> 1924 Las Lomas NE
> Albuquerque NM 87131-0001
> Phone: (505) 277-8892
> Fax: (505) 277-7108
> thomas@mgt.unm.edu
> http://www.unm.edu/~thomasd
> 

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