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st: Regression Equation for Zero inflated negative binomial


From   rachel grant <rachelannegrant@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Regression Equation for Zero inflated negative binomial
Date   Mon, 19 Sep 2011 09:54:29 +0100

Thank you for your help. Maybe I need to explain the problem more clearly
I have used Zero Inflated negative binomial regression in Stata to
model some overdispersed, zero inflated count data. I got very nice
results and also used the postestimation tools to predict Y values.
This is included in my PhD thesis which I am about to submit. My PhD
supervisor said as well as presenting the results (i.e cofficients, p
values etc.) I also have to show "the model". I think by this he means
the regression equation in the form:

natural log (Y) = B0+B1X1 + B2X2..............

I cannot find out what the equation is for ZINB models and also I
cannot find out how to make Stata display this model.
I could just add in the coefficients myself BUT I am not sure of the
exact formula of the model for ZINB (especially the ZI part) as I
think it may be more complicated than the simple Poisson

log e  (Y) = β0 + β1Χ1 + β2Χ2 ...

I have searched everywhere to find a general equation for ZINB with no
luck and also read all the Stata help files.
I am very confused about why this seemingly simple thing should prove
so impossible! I am a beginner with stata, and previously only used
simple linear regression so thank you for your patience.

-- 
regards, Rachel Grant

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