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Re: st:appropriate test

From   Steve Samuels <[email protected]>
To   [email protected]
Subject   Re: st:appropriate test
Date   Fri, 8 Oct 2010 14:26:00 -0400


 Rajaram Subramanian Potty

I recommend that you add all the sampling stages to your design.
Include fpcs, especially in the first stage, because you need all the
help that you can get in reducing standard errors.

something like:
svyset psu [pweight=], strata(place) fpc() || _n, strata(round) fpc()

One thing is unclear: the sampling frame you used to select males and
females. If your sampling frame consisted of households, for example,
then replace "_n" in the -svyset- statement above with the household
id variable.

Which analysis?

As you describe your analysis, it is descriptive (or "enumerative"):
you want to estimate prevalence rates in one district in 2003 and 200,
and their difference.

For a descriptive analysis, significance testing is inappropriate.
Why? If you had  tested every adult in the district, you would never
expect the 2002 and 2008 prevalence rates to be _exactly_ the same.
(WG Cochran, (1977). Sampling techniques (3rd ed.). New York: Wiley.,
p.39; WE Deming. (1966). Some theory of sampling. New York: Dover
Publications, Chapter 7, p 247, "Distinction between enumerative and
analytic studies").

(There are descriptive studies where hypothesis testing is important,
e.g. quality assurance sampling ( P Levy and S Lemeshow, Sampling of
Populations, Wiley, 2008; p. 429), but your study doesn't seem to be
one of them. )

The question is therefore not "Are rates in the two years different?",
but "How different are ?" Confidence intervals provide the answer.

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