Re: st: generating std. devs. using svyset

[Kristin MacDonald <kmacdonald@stata.com>]

Leslie Hinkson <lhinkson@Princeton.EDU> asked about calculating standard
deviations when working with survey data.  One way she can obtain the
population standard deviation is to estimate the mean of the variable using
-svy:mean-.  This command returns a matrix e(V_srs) that contains an 
estimate
of the variance assuming data were collected from a simple random sample
without replacement.  The formula for V_srs is

       V_srs = (s^2) / n

Therefore, we can use this value along with the sample size in e(N) to 
obtain
an estimate of the population standard deviation.  Here is an example.

       webuse nhanes2, clear
       svyset
       svy: mean height
       di "standard deviation = " sqrt(e(N) * el(e(V_srs),1,1)

It turns out that this standard deviation can also be calculated by
-summarize- with aweights.  For further details on this, see

       http://www.stata.com/support/faqs/stat/supweight.html

-- Kristin
kmacdonald@stata.com


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