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# Re: st: RE: Calculating SD of a variable

 From Maarten Buis To statalist@hsphsun2.harvard.edu Subject Re: st: RE: Calculating SD of a variable Date Wed, 19 Oct 2011 15:19:09 +0200

```On Wed, Oct 19, 2011 at 2:58 PM, lreine ycenna wrote:
> Hi, I forgot to respond to this, and now this problem's come back to
> me. I udnerstand now that using -egen SD= sd(gdp), by(country year) -
> generates missing observations, but how can I then calculate SD
> according to both country and year? (i.e. no repeated sd for each year
> or each country).

The standard deviation measures how different a set of values are from
one another. Since, you want to compute the standard deviation by
country and year you have per standard deviation only one value for
which to measure differences across values, that is obviously hard
(actually it is easy: someone does not differ from itself, so the
standard deviation is trivially 0). So you'll probably need to rethink
what you want to do.

Hope this helps,
Maarten

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

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