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


From   Suzy <scott_788@wowway.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Again-Unique Case ID in Large Panel
Date   Wed, 04 Aug 2004 13:41:15 -0400

To show an example:

Duplicates in terms of ID

--------------------------------------
copies | observations surplus
----------+---------------------------
1 | 9910 0
20 | 100 95
21 | 336 320
--------------------------------------

This output is mine. It states that I have 5 observations with 20 copies each (100/2) and 16 observations with 21 copies each (336/21) for a total of 21 (16 + 5) subjects (observations) that have multiple duplications.



Suzy wrote:


...the 'one copy' refers to the observations (1322511) actually in the dataset.

Suzy wrote:


I believe that your output is saying that you have one copy of 1322511 with no surpluses (no duplicates). I just ran this yesterday with my much smaller dataset and was able to verify this.
Suzy

Stephen V. Burks wrote:


Hi, Folks.

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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