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Re: st: drop command & missing values


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: drop command & missing values
Date   Mon, 12 Oct 2009 03:11:06 -0700 (PDT)

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------


--- On Mon, 12/10/09, Francesco Trivieri wrote:
> when I drop some observations by writing:
> 1) drop if x>123
> Stata drops also the missing values of the x
> variable.  When I use the following
> 2)  drop if x>123 & x!=.
> Stata does not drop the missing values
> As missing values are discarded in any estimations, Stata
> should consider the same obsevations whather command I use
> (1 or 2). By constrast, the number of obsevations  is
> much smaller when I run a regression after using the command
> 1)

Stata ignores observations with missing values on x only when
you use it in your estimation, so which command you use will
matter if your estimation command is something like
-regress z w z- (so, no x) .

Hope this helps,
Maarten

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