ROBERT BOZICK <[email protected]> is concerned abou the 'Number of obs'
output in the header of -svymean- (replaced by -svy: mean- in Stata 9):
> I am working on a project where I need to use survey commans to estimate the
> standard error correctly --- my sample uses a stratified cluster design. I
> created a variable called samp to indicate the analytic sample. When samp =
> 1, then the respondent will be included in the analysis; when samp = 0 then
> the respondent will not be included in the analysis.
>
> The frequency of samp is shown below:
>
> tab samp
>
> samp | Freq. Percent Cum.
> ------------+-----------------------------------
> 0 | 6,917 42.25 42.25
> 1 | 9,456 57.75 100.00
> ------------+-----------------------------------
> Total | 16,373 100.00
>
> As you can see, there should be 9,456 in my analysis.
> When I use the svy commands to estimate means for my analytic sample using
> the subpop command, the output reports that there are 15,548 used in the
> analysis. Intuitively, that cannot be correct. Does anyone know what is
> going on here? How can I fix this so that it reports 9,456 instead of
> 15,548? Thanks!
>
> svymean var1, subpop(samp)
>
> Note: 11 strata omitted because they contain no subpopulation members
>
> Survey mean estimation
> pweight: f1pnlwt Number of obs = 15548
> Strata: strat_id Number of strata = 350
> PSU: psu Number of PSUs = 729
> Subpop.: samp==1 Population size = 3312561.5
> ------------------------------------------------------------------------------
> Mean | Estimate Std. Err. [95% Conf. Interval] Deff
> ---------+--------------------------------------------------------------------
> var1 | 46.72176 .2878163 46.15584 47.28768 4.473885
> ------------------------------------------------------------------------------
In Stata 8, unlike -svyregress-, -svymean- does not display the subpopulation
sample size. However Robert could use -svyregress- to compute a subpopulation
mean
. svyregress var1, subpop(samp)
and have the subpopulation size and its sample size get reported in the
header. Note that the subpopulation mean estimate and its standard error are
the same whether you use -svymean- or -svyregress-.
In Stata 9, all the -svy- estimation commands have a unified header, and this
header includes the subpopulation size and its sample size too. The Stata 9
syntax, using Robert's example is
. svy, subpop(samp) : mean var1
--Jeff
[email protected]
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