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Re: st: Mixed effects model with zero-inflated negative binomial outcome for repeated measures data


From   W Robert Long <W.R.Long@leeds.ac.uk>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Mixed effects model with zero-inflated negative binomial outcome for repeated measures data
Date   Sun, 13 Jan 2013 16:04:35 +0000

Thank you.

I did, however, have the impression that -gllamm- does not support the negative binomial distribution ?

I have looked through the http://www.gllamm.org/examples.html page and I didn't see any mention of zero-inflation. I also looked through the review article http://www.bristol.ac.uk/cmm/learning/mmsoftware/reviewgllamm.pdf and didn't find it mentioned there either.....

Do you have any reference, or other information, about the possible collinearity problem ? I assume this refers to correlation of random effects in the binomial probabilities part and the mixture-model part ? It would, of course, be ideal if it were possible to fix one of these REs to zero, and/or the correlation to zero, but to allow the model to estimate this correlation would also be OK !

Thanks again.

Robert Long


On 13/01/2013 00:05, JVerkuilen (Gmail) wrote:
On Sat, Jan 12, 2013 at 1:43 PM, W Robert Long <W.R.Long@leeds.ac.uk> wrote:

Is it possible to fit this kind of model in Stata ? If so, could you provide
some pointers ?
I believe you could specify such a model in -gllamm- and seem to
recall that one of the examples on the web page compare Poisson, NB,
ZIP and ZINB, but if you look at http://www.gllamm.org/examples.html
the examples are there for you.

That said, I suspect that a ZINB with mixed effects would be a pretty
tough model to estimate well in nearly any package given that the NB
overdispersion parameter, overdispersion created by zero inflation,
and overdispersion created by clustering are all likely to be highly
collinear.
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