Re: st: GSAMPLE R3300

[Lucas <lucaselastic@gmail.com>]

Why not simply remove the certainty units (C Units), draw the sample
from the remainder units (R Units) to obtain the sampled units (S
Units), then add the certainty and sampled sets (C & S) together to
form the final sample (FS units)?

Sam

On Thu, Sep 6, 2012 at 8:44 AM, Stas Kolenikov <skolenik@gmail.com> wrote:
> On Thu, Sep 6, 2012 at 9:28 AM, Lieke Boonen (SiRM)
> <Lieke.Boonen@sirm.nl> wrote:
>> We try to take a sample from our population, without replacement. we have several subgroeps with a high sampling weight. However with the gsample command it gives an error because for these cases the w_i*n /sum(w) is lager than 1. We thought the program looked at the relation between the weights and that this should not be a problem. Does anyone recognize this problem and is there a solution for this problem?
>
> As far as I can recall, -gsample- does a decent job of selecting one
> observation from the list, provided, as you found the hard way, that
> you don't have any certainty units. However, it is not appropriate for
> many real situation sampling problems, which usually require more
> complicated code. You also need to be aware that PPSWOR is a very
> non-trivial and counter-intuitive task. See
> http://www.citeulike.org/user/ctacmo/tag/unequal_prob_sampling for the
> appropriate references. All in all, you probably need to do this:
>
> 1. Identify the certainty units, set their probability of selection to 1.
> 2. Adjust the probability distribution, pulling up the probabilities
> for other units.
> 3. Check again for the certainty units: repeat steps 1-2 until the
> probability of selection on a single draw have converged.
> 4. Implement your PPS procedure -- systematic sample is the poor man,
> old days shortcut procedure to sample from the physical list on
> sheet(s) of paper that leads to technical difficulties in variance
> estimation; Rao-Hartley-Cochran is the easiest-to-implement shortcut
> that leads to an approximate PPS; Rao-Sampford used to be the most
> rigorous choice until Tille's elimination procedures appeared in the
> literature.
>
> --
> -- 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
>
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