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Re: st: suggested references about the variables to include in zero-inflated portion of zinb?


From   Steven Samuels <sjhsamuels@earthlink.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: suggested references about the variables to include in zero-inflated portion of zinb?
Date   Fri, 24 Oct 2008 08:45:10 -0400

What justification did you have for the variables in the non-inflated part? Obviously you had some theory or previous empirical work to guide you. The same justification would apply to variables in the inflated-part. Previous work may have only stated that "Z is associated with psychological stress." The beauty of ZINB is that it elaborates somewhat the mechanism of the association.

If you chose predictors (inflated AND non-inflated) from a much larger set, based on their statistical significance, that part of your analysis is exploratory. If you do not validate your predictors on a new set of data, after-the-fact justifications will always be suspect.

-Steve

I am using zinb to estimate level of psychological distress (scores range from 0-24) using various demographic variables and measures of use of the Internet. I've used -countfit- to compare various count models and the results support zinb as the best fitting model.

I am uncertain, however, about how to justify the variables that I include in the zero-inflated part of the model. I've read journal articles that have used zinb, read the book by Freese and Long, and searched the Internet and Statalist but I have not been able to find any detailed recommendations or procedures. Can anyone suggest any other sources (books or journals) that provide an explanation or a good example of this process?

Ideally I would like to find a good source that I can cite in the paper -- but I appreciate any suggestions about this you might have.

Thanks for you help,
Tim

-----------------------------------------------------
Timothy M. Hale, MA
Graduate Assistant
University of Alabama at Birmingham
Department of Sociology
email:  timhale@uab.edu

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