st: Re: sum of missing values returned as zero

["Martin Weiss" <martin.weiss1@gmx.de>]

Note -egen, total- where you can add the -missing- option to toggle this 
behavior back and forth...

HTH
Martin
_______________________
----- Original Message ----- 
From: "Jacob Wegelin" <jwegelin@vcu.edu>
To: <statalist@hsphsun2.harvard.edu>
Sent: Saturday, October 04, 2008 12:44 AM
Subject: st: sum of missing values returned as zero



> The following code
>
> clear set obs 4
> gen Finished=.
> list
> summarize Finished
> return list
>
> returns a value of zero for the sum of Finished, as is seen below.  I do 
> not understand. I would think that the sum of a list of numbers, at least 
> one of which is missing, would be missing, not zero. Can someone explain?
>
> . set obs 4
> obs was 0, now 4
>
> . gen Finished=.
> (4 missing values generated)
>
> . list
>
>      +----------+
>      | Finished |
>      |----------|
>   1. |        . |
>   2. |        . |
>   3. |        . |
>   4. |        . |
>      +----------+
>
> . summarize Finished
>
>     Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>     Finished |         0
>
> . return list
>
> scalars:
>                   r(N) =  0
>               r(sum_w) =  0
>                 r(sum) =  0
>
>
> Thanks
>
> Jacob A. Wegelin
> jwegelin@vcu.edu Assistant Professor
> Department of Biostatistics
> Virginia Commonwealth University
> 730 East Broad Street Room 3006
> P. O. Box 980032
> Richmond VA 23298-0032
> U.S.A. http://www.people.vcu.edu/~jwegelin
>
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