Peter Flom
2004-Oct-09 16:00 UTC
[R] RE: zero-inflated count models (was polr problem solved)
John Fox wrote <<<>From your description, it seems possible that there are too many zerosfor a Poisson or negative-binomial model. Since the focus of your paper is the methodology, you might want to try a zero-inflated Poisson or negative-binomial model. Though I haven't tried them, I'm aware of two sources of R functions for zero-inflated count models -- zeroinfl(), from Simon Jackman's web site <http://pscl.stanford.edu/content.html>, and gnlr() in Jim Lindsey's gnlm package, which is not available on CRAN but at <www.luc.ac.be/~jlindsey/rcode.html>.>>>Indeed. I am going to use these, as well, and attempt to demonstrate that fitting the correct model not only is correct, statistically, but also give results that are substantively different than the 'usual' models. I hope that this will increase the use of appropriate models in the field (which, in case anyone is interested, is substance abuse research, and, in my particular case, the syringe-sharing behaviors of drug injectors). Peter Peter L. Flom, PhD Assistant Director, Statistics and Data Analysis Core Center for Drug Use and HIV Research National Development and Research Institutes 71 W. 23rd St www.peterflom.com New York, NY 10010 (212) 845-4485 (voice) (917) 438-0894 (fax)