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st: RE: Again-Unique Case ID in Large Panel


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Again-Unique Case ID in Large Panel
Date   Wed, 4 Aug 2004 18:28:18 +0100

I see no inconsistency here as far as -duplicates- 
is concerned. 

-duplicates report- is telling you that, in terms of these 
two variables, there are 1322511 observations, each of which is 
unique. Thus, none are surplus, in the sense of repeating 
information. That is, no duplicates, as -duplicates list- is also 
telling you. 

I cannot solve the -xtdes- mystery. 

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

Stephen V. Burks
 
> Now I wonder if I am reporting a bug.  As per Nick's suggestion
> (thanks, Nick) I looked up -duplicates- and ran it.
> 
> Results:
> (1) using -duplicates report-
> 
> . duplicates report  DRVNUM  CDATE
> 
> Duplicates in terms of DRVNUM CDATE
> --------------------------------------
>     copies | observations       surplus
> ----------+---------------------------
>          1 |      1322511             0
> --------------------------------------
> 
> (2) using -duplicates list-
> 
> . duplicates list  DRVNUM  CDATE
> Duplicates in terms of DRVNUM CDATE
> (0 observations are duplicates)
> 
> 
> If I read this correctly, one version of -duplicates- says I have
> a single duplicate (the last case in the file), while the other
> says I have none. Also, -xtdes- still says that DRVNUM and
> CDATE do not uniquely identify cases.
> 
> I looked in the data browser, and the last case is NOT a duplicate.
> While DRVNUM is the same as the case before, CDATE is not.
> 
> If my interpretation of the output is correct then my best guess is
> that -xtdes- is wrong to say I do not have unique identification,
> and whatever bug causes this might also be behind the apparently
> incorrect response from -duplicates report-.  In any event, it seems
> to be a problem that -duplicates list- and -xtdes- do not agree.
> 
> Any better ideas?
> 
> Thanks,
> Steve
> 
> P.S. My version of Stata is 8.2 for WinXP, with current updates.

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