Vivian Hoffmann <veh4@cornell.edu> has a couple of questions about -svy: mean-:
> I'm computing means using svy: mean and I'm puzzled by two things:
>
> 1. The number of observations reported with the summary statistics is
> generally smaller than the number of observations in my sample (or
> subsample). This is the case even when I know the data on the variables to
> be summarized are complete for these observations.
Stata's survey estimation commands will drop observations from the estimation
sample for any of the following reasons:
1. One or more variables of interest contain a missing value. This
include the -svyset- variables and variable supplied to options, such
as -subpop()-, -over()-, -stdize()-, and -stdweight()-.
2. With the -subpop()- option, entire strata are dropped when they do
not overlap with the specified subpopulation.
> 2. For some sub-populations I get the following error message:
>
> Note: Missing standard error due to stratum with single sampling unit; see
> help svydes.
>
> So I omit the observations which are singletons within a stratum. But I
> continue to get the same error. The error disappears when I drop some of
> the variables to be summarized.
The note is pointing out that one or more strata in your dataset contain only
one sampling unit.
Use
. svydes if e(sample)
to find out which of your strata contain only one sampling unit whenever -svy:
mean- (or any other -svy- command) produces this note.
--Jeff
jpitblado@stata.com
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/