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Re: st: Zero Inflated Negative Binomial model


From   Richard Williams <richardwilliams.ndu@gmail.com>
To   statalist@hsphsun2.harvard.edu, "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Zero Inflated Negative Binomial model
Date   Fri, 20 Jan 2012 10:06:37 -0500

At 08:02 AM 1/20/2012, Eugene Walls wrote:
I am working with a dataset that contains counts of the number of times that youth in the sample engage in self-harming behaviors (such as cutting). My co-authors and I are interested in using the zero-inflated negative binomial models because (a) we have a sample that has about 74% zeroes and (b) because we are conceptualizing two processes occurring - one that predicts the likelihood of crossing the threshold into self-injurious behavior and one that predicts the number of times of engaging in the behavior. The Vuong test seems to indicate that the ZINB model is a better fit for the data than the NBReg model.

Our question concerns if it is appropriate to use the ZINB because the response set of the variable capturing the number of times of engaging in SIB is not a straight count, but rather a "0 times" "1 time" "2-3 times" "4-5 times" "6-10 times" "11-20 times" "21-49 times" "50 or more times". We have recoded the variable into 0, 1, 2, 4, 6, 11, 21, 50 using the minimum in the category.but if we do that is using the ZINB model problematic?

Thanks
Eugene

I have a feeling it won't work well but you could try intreg. The manual entry shows how to test whether intreg is working ok or if an ordered probit is preferable.

Whatever you do you might try some sensitivity analyses, e.g. are your results radically different if you use the low end, the midpoint, or the high end of an interval?


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Richard Williams, Notre Dame Dept of Sociology
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