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

[Steven Samuels <sjhsamuels@earthlink.net>]

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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