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Re: st: -svy- commands with a pps sample vs. a simple random sample

From   Stas Kolenikov <>
Subject   Re: st: -svy- commands with a pps sample vs. a simple random sample
Date   Sat, 14 May 2011 08:44:16 -0500

On Sat, May 14, 2011 at 3:33 AM, Nick Cox <> wrote:
> Stas' initial statement is incorrect if the sense of "black box" is
> that you can't see the detailed code. The source code for
> -mm_sample()- is accessible once you have installed the -moremata-
> package. Example code below. There are calls to other functions.
> The user-written commands referred to, -moremata- and -gsample-, are from SSC.

Oh, I see (-help moremata_source-). The code in -mm_ups*()- is only
good for drawing one unit from with probability proportional to a
measure of size. If you are drawing more than one unit, you won't get
PPS, although your actual probabilities of selection will be
correlated with the measure of size. I suspect that the more you draw,
the farther you'll be from PPS. But this is a tangential issue; the
more relevant one is the more subtle explanation about what it is that
PPS is able to bring down: the largest residuals in the case when the
magnitude of residuals is correlated with size.

Stas Kolenikov, also found at
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