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st: Overdispersed poisson regression


From   Lynsey Patterson <Lynsey.Patterson@hscni.net>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: Overdispersed poisson regression
Date   Mon, 5 Sep 2011 10:55:11 +0000

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________________________________


Dear Statalist,

I am interested in analysing the trend in rates of meticillin resistant S. aureus (MRSA) for my region. I have several variables to include in the model – time (the year (1) and the quarter (2)), the number of episodes (3), the number of occupied bed days (the denominator (4)) and the Trust (a measure of geography (5)).

When I summarize the rate I get a mean of 0.127/1000 bed days with a variance of 0.008. So I think a normal poisson model cannot be fitted and I need to use an over dispersed? I have read about a command for negative binomial regression – does anyone know if this is correct and what syntax I should use?

E.G. nbreg number of episodes (3) year(1) quarter(2) trust(5), exp(occupied bed days (4))

Thanks in advance for any advice.

Lynsey

________________________________



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