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Re: st: artifacts after merge


From   Louis Boakye-Yiadom <lby_kw@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: artifacts after merge
Date   Mon, 29 Oct 2007 14:16:01 +0000 (GMT)

I believe where a non-matching variable in the two
datasets have different values, the master dataset's
values supersede that of the using dataset. In your
case, I suspect KP was your master dataset.

Louis


--- Michael McCulloch <mm@pinest.org> wrote:

> Dear Statalist members,
> I am merging two datasets, KP.dta and PS.dta, which
> were sorted by 
> the variable <id>. They contain the subjects who
> from two different 
> exposure groups.
> 
> Values for <id> are unique to each dataset, so that
> <id> occurs only 
> once in each dataset, and are not duplicated across
> datasets.
> 
> Before the merge,
> 	In dataset KP, one variable <smoker> has values yes
> or no: 1/0.
> 	In dataset PS,  <smoker> is missing.
> However, after the merge, PS now has values for
> <smoker>.
> 
> I merged using this command:
> 	use "A.dta", clear
> 	merge using "B.dta"
> 
> Then, checked my data:
> 
>         id   group   smoker
>          1      PS        1
>          2      PS        1
>          3      PS        1
>          4      PS        0
>          5      PS        0
>          6      PS        1
>          7      PS        1
>          8      PS        1
> 
> What have I done wrong?
> Thank you kindly.
> 
> 
> -- 
> 
> Michael McCulloch
> Pine Street Foundation
> 124 Pine St., San Anselmo, CA 94960-2674
> Tel:	(415) 407-1357
> Fax:	(415) 485-1065
> mcculloch@pinestreetfoundation.org
> 
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> 


--------------------
Louis Boakye-Yiadom
34 Holloway
Bath
BA2 4PU
Phone (home): (44)-(0)1225-427699
Phone (mobile): (44)-(0)795 609 3780


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