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Re: st: svy adjustment for rates


From   Steven Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: svy adjustment for rates
Date   Tue, 22 Feb 2011 08:57:17 -0500

 
Sujit Rathod -


Sujit-

"And while I can run something like -svy: ratio deaths/survival_time- these do not give me the correct (Poisson?) CIs."

Absolutely incorrect.  Survey-adjusted standard errors are based not on the Poisson assumption, but on the repetitions of the sampling procedure. To see why, I recommend a good sampling text such as Sharon Lohr, Sampling: Design and Analysis, Duxbury, 1999 and 2009.

Below is code. The point estimates are the same, but I would prefer the result from -svy: poisson-, because it gives asymmetric CIs based on the log of the ratio.

*******************
sysuse auto, clear
svyset _n

svy: ratio rep78/turn, over(foreign) 

xi, noomit: svy: poisson rep78 i.foreign, nocons exposure(turn) irr
xi, noomit: svy: nbreg   rep78 i.foreign, nocons exposure(turn) irr
*********************** 

Steve

Steven J. Samuels
Consultant in Statistics
18 Cantine's Island
Saugerties, NY 12477 USA
Voice: 845-246-0774
Fax:   206-202-4783 
sjsamuels@gmail.com



On Feb 21, 2011, at 1:30 AM, Sujit Rathod wrote:

I am using Stata 10.1, and am analyzing data from a population-based
household survey of mortality in the past 12 months.

I have data on the length of survival in the past 12 months for every
household member, and would like to calculate mortality rates by
different characteristics (eg sex, age etc).

While I can calculate non-survey-adjusted mortality rates using
-strate-, this does not work with the -svy- prefix. 



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