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Re: st:appropriate test

From   Ronan Conroy <[email protected]>
To   "[email protected]" <[email protected]>
Subject   Re: st:appropriate test
Date   Wed, 6 Oct 2010 09:59:40 +0100

On 6 DFómh 2010, at 07:42, Rajaram Subramanian Potty wrote:

I have data from two rounds of survey conducted in the same areas
(PSUs). But the individual are selected independently in both the
rounds from these areas using the same statistical approaches. What
would be the appropriate analysis that would be carried out to test
the difference in some of the indicators between the two periods. For,
example I want to test the difference in HIV prevalence between the
two rounds. Is it appropriate to use the survey command by considering
the PSUs are the same in both the rounds and setting the survey design
according to our study. After that fitting svy: logistic to examine
the difference in two rounds, is this correct way of testing the
difference between the two rounds. Kindly suggest.

My first reaction would be that the most important thing needed here is a sample weighting scheme that allows you to extrapolate from the sample to the underlying population.

Are the areas PSUs or strata? In other words, were the areas selected at random or deliberately chosen? This affects your analysis.

If you have presumed age of infection, you could consider using an event-time model approach, using age as the time variable. This would allow you to look at the shape of the hazard function. Even if you don't, the hazard curve will show the cumulative prevalence by age (rather than the incidence) but may still be of interest.

Ronán Conroy
Associate Professor
Division of Population Health Sciences

[email protected]
Royal College of Surgeons in Ireland
Epidemiology Department,
Beaux Lane House, Dublin 2, Ireland
+353 (0)1 402 2431
+353 (0)87 799 97 95
+353 (0)1 402 2764 (Fax - remember them?)

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