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Re: st: svyset


From   Stas Kolenikov <skolenik@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: svyset
Date   Fri, 2 Nov 2012 07:18:35 -0500

This design took a lot of compromises. Systematic sampling is THE
worst sampling procedure, and the only excuse for using it is that you
only had access to paper, and could only do a long addition on the
margin of the printout of your list of EAs with cumulative population
sizes. Still, systematic sampling could hit some large units (larger
than {the total population size}/{# of units sampled}) more than once,
so it could have worked effectively with replacement (which is what
you want, without replacement is tedious to work with).

The finite population correction is only relevant for SRS. It does not
generalize well to PPS type designs, where, technically speaking, you
should use double probabilities of selection (and if you find yourself
doing that, you would recall that the systematic sampling does not
allow unbiased variance estimation... that's why I said it is the
worst method).

You are correct regarding strata2: you'd have to create an indicator
for the type of the HH.

-- 
-- Stas Kolenikov, PhD, PStat (SSC)  ::  http://stas.kolenikov.name
-- Senior Survey Statistician, Abt SRBI  ::  work email kolenikovs at
srbi dot com
-- Opinions stated in this email are mine only, and do not reflect the
position of my employer

On Fri, Nov 2, 2012 at 6:06 AM, Rebecca Pietrelli
<rebecca.pietrelli@gmail.com> wrote:
> Hi,
>
> I really hope anyone can help me.
> I am using the Stata command svyset in order to declare the survey
> design to files of my dataset (Uganda Migration Housolds Survey 2010).
>
> The sampling design is two-stage stratified.
> In the first stage: enumeration areas - EAs - (PSU) were selected,
> separately for rural and
> urban areas. The applied procedure is a PPS (proportionally done based
> on the number of households in the respective stratum according to the
> 2006 Uganda household survey) combined with a systematic approach.
> In the second stage: households were selected in each EA, using a
> systematic procedure (4 hhs with international migrants, 3 with
> internal migrants and 3 without migrants).
>
> I think to use the following command:
>
> svyset psu_var [pw=hhweights_var], strata(strata1_var) fpc(fpc1) ||
> _n, strata(strata2_var) fpc(fpc2).
>
> I have the following doubts:
>
> 1) I am not sure if the first stage is with or without replacement (It
> is not mentioned in any part of the report!!!). I suppose that a PPS
> combined with a systematic procedure is without replacement. Is this
> assumption correct?
>
> 2) I have the strata1_var (rural or urban) but I don't have the
> strata2_var. In that case, should I create it? (for ex. strata2 = 1 if
> hh does not have migrants, = 2 if it has internal migrants and = 3 if
> it has international migrants).
>
> 3) I don't have fpc in the data. I think to create them as
> [(N-n)/(N-1)]^(1/2). So in the first stage, is N the total number of
> EAs in Uganda or is it the total number of hhs living in Uganda?
>
> Thank you very much for your help and time.
> Rebecca
>
>
>
>
> Thank you very much for any help.
> Rebecca
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