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st: drop command & missing values


From   "Francesco Trivieri" <francesco.trivieri@unical.it>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: drop command & missing values
Date   Mon, 12 Oct 2009 11:48:46 +0200

dear users,
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)
thank you
Francesco
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