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st: RE: Unique Case ID in Large Panel


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Unique Case ID in Large Panel
Date   Wed, 4 Aug 2004 17:27:40 +0100

i can't see what the problem is, but, 
as in another thread, -duplicates- offers
a way to tackle this. You don't need
to write your own code, good exercise
though that is. 

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

Stephen V. Burks
> 
> My problem is that -xtdes- says my two key variables do not together 
> uniquely identify the cases in my large panel data set, but 
> both the Stata 
> code I wrote to identify the duplicates, and SPSS's 
> automatically generated 
> syntax to "find duplicates" (operating on a precursor data 
> set with the 
> same cases and variables) say there are no duplicates.
> 
> Searching the FAQs on "xtdes" produced no hits.
> 
> Specifics:
> 
> 1) I have 1,322,511 cases.   The data set is about 700 MB.  Memory 
> allocated is 1.4GB (and wasn't it a kick in the fatoozle to 
> discover that's 
> all WinXP will let me allocate from the 4 GB on my system!).
> 
> 2) I first did -tsset- using DRVNUM (employee id) and CDATE 
> (paycheck date).
> 
> 3) -xtdes- message:
> 
>    DRVNUM:       10001, 10003, ..., 99051                          n 
> =      28946
>    CDATE:        15344, 15351, ..., 16072                          T 
> =        105
>             Delta(CDATE) = 7; (16072-15344)/7 + 1 = 105
>             (DRVNUM*CDATE does not uniquely identify observations)
> 
> 4) Stata Code run on data to find duplicates:
> . gsort +DRVNUM +CDATE, generate(DriverWeek)
> . generate DupDriverWeekFlag=0
> . replace DupDriverWeekFlag = 1 if ( DRVNUM == DRVNUM[_n-1] & 
> CDATE == 
> CDATE[_n-1] )
>   (0 real changes made)
> 
> 5) -summarize- run on DupDriverWeekFlag says min and max are both 0.

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