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Re: st: Collapse with sum function and missing values


From   Kit Baum <baum@bc.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Collapse with sum function and missing values
Date   Wed, 10 Feb 2010 10:06:30 -0500

<>
This is somewhat semantic. The presence of 3 and 4 in the group id suggests that such groups exist; they merely have no members in the present sample. It should be easy enough to -mvdecode- x==0 to x==.

This reminds me of a grouse I had about the calculation of the s.d. of data that were all missing. The mean of these data was computed properly as missing, but the s.d. was reported as 0. Pedantically, as all values took on the same NAN value, there was indeed zero variance. I convinced StataCorp that this was not a good idea, and that the s.d. or variance of data that are all missing is indeed missing. That is now what -tabstat- does.

Kit
 
On Feb 10, 2010, at 2:33 AM, Michael wrote:

>  Shouldn't the value of -x- for groups 3 and 4 be missing, not zero.
> To me, the sum of a series of missing values is a missing value. I am
> doing a collapse for about 100 variables (100 x values) and need the
> value to be defined as missing (not 0) in such cases. Any ideas?


Kit Baum   |   Boston College Economics & DIW Berlin   |   http://ideas.repec.org/e/pba1.html
                              An Introduction to Stata Programming  |   http://www.stata-press.com/books/isp.html
   An Introduction to Modern Econometrics Using Stata  |   http://www.stata-press.com/books/imeus.html


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