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Re: st: Missing observations


From   David Hoaglin <dchoaglin@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Missing observations
Date   Thu, 20 Jun 2013 07:20:41 -0400

Simply dropping missing values or, more commonly, dropping
observations in which the value of any variable is missing requires
careful consideration of the reasons that are responsible for those
values' being missing.  In the mechanism underlying the "missingness"
does not satisfy certain assumptions, using only the "complete cases"
or the available data can lead to serious bias.  The topic of missing
data has a large literature, including the book by Little and Rubin
(2001).

David Hoaglin

Little RJA, Rubin DB (2001).  Statistical Analysis with Missing Data,
2nd ed.  Wiley.

On Thu, Jun 20, 2013 at 6:17 AM, Csaba Kertai
<csaba.kertai@hotmail.co.uk> wrote:
> Dear All,
>
> I need a bit of help with dropping missing observations. If I use 'drop if missing(var)' or drop if 'var'==. etc. many other observations are dropped as well. More precisely, var1 has 1125 observations and var2 has 169 observations. I want to drop missing observations for var2 but if I use drop if var2==. then this will keep only 169 observations for each variable. I only want to drop values that are missing.
>
> Any help is greatly appreciated.

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