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RE: st: RE: -finddup- for panel?


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: -finddup- for panel?
Date   Wed, 21 Apr 2004 11:24:49 +0100

If observations are duplicates, the choice of 
which to keep can be difficult... 

-duplicates- arrived with Stata 8. Some 
users were already in the habit of using 
various user-written programs published
in the STB or on SSC, including -unique-, 
-finddup-, -dups- and various others.  
If they serve your purpose, fine. 

But you no doubt are aware that observations
can be duplicates with respect to some 
variables -- in your case -id- and -year- --
but differ with respect to other variables. 

-finddup- offers no facilities for dropping 
duplicates. It is an inspection program, 
and gives information which can be used
to decide on what to -drop-. 

The intent of -duplicates- is to provide
a more general tool, including functionality
for -drop-ping duplicates. But -duplicates- 
will not let you go 

. duplicates drop id year 

whenever other variables also exist. You 
must spell out 

. duplicates drop id year, force 

as a reminder that you may be losing information. 
In this way -duplicates- is designed to be 
potentially destructive, but also to inhibit 
accidental loss of real information. 

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

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of joe J.
> Sent: 21 April 2004 11:08
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: RE: -finddup- for panel?
> 
> 
> Stata's official -duplicates- command also helps to identify 
> duplicate 
> observations. But I have a feeling that -finddup- is useful 
> when one has to 
> decide over which among the duplicates to include and which 
> to exclde  (for 
> late use, say) while generating a dupliate-free data set.
> 

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