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Re: st: Selecting a sample to compromise between significant size and geographical dispersion


From   Maarten Buis <maartenlbuis@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Selecting a sample to compromise between significant size and geographical dispersion
Date   Thu, 15 Sep 2011 10:06:18 +0200

On Thu, Sep 15, 2011 at 9:25 AM, Partho Sarkar wrote:
> Broadly speaking, I want to select a sample from a very large
> population to achieve a "good" compromise between excluding
> "insignificant" units, and ensuring "reasonable" diversity.  I have a
> hierarchical dataset on prices of some commodities from markets across
> the country.  (The geographical levels being:
> national-state-district-market.  Markets are the primary units). I
> want to consider the prices only from "significant" markets, i.e., for
> each commodity, markets which have trading volumes at least equal to
> the median volume (say).  BUT, I also want to ensure as complete a
> geographical coverage as possible.

What is the population that you want to generalize to? My suspicion is
that as soon as you have defined that, you'll see that there is no
trade-off. For example: if the population of interest is markets with
more than median trading volume than the geographic dispersion is
given by that constraint. Having two conflicting criteria suggests to
me that your definition of the population is still too fuzzy.


Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany


http://www.maartenbuis.nl
--------------------------
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