Sure, Phil. I'll just post here.

I would start with:

- Gardener,W., Mulvey, E.P., Shaw, E.C. (1995) Regression Analyses of Counts and Rates: Poisson, Overdispersed Poisson, and Negative Binomial Models. Psychological Bulletin.

- Long, J.S. (1997) Regression Models for Categorized and Limited Dependent Variables. Thousand Oaks, CA: Sage Publications.

- Long, J. Scott & Freese, Jeremy. (2006). Regression Models for Categorical Dependent Variables Using Stata, Stata Press.

The Gardener article is a brief overview. It doesn't have anything about ZIP, but is easy to read and a great place to start if you're new to the topic. It does have Poisson and Negative Binomial.

The Long book is fabulous, but gets a little mathy. He is a sociologist, so it is definitely written for researchers, not statisticians. But there is calculus and linear algebra in places. This is the best place to find indepth info, esp. ZIP.

The Long and Freese book is more applied, less math. I would recommend it even if you don't use Stata.

Because I get asked for resources so often, I created a list of my favorite ones for many topics at:

http://www.analysisfactor.com/resources/Top-Resources.html. I pulled these right out of it. To get it, you have to sign up, but you can always unsubscribe if you're not interested.

And it just happens my next teleseminar is on Poisson and Negative Binomial Regression. It's on Jan 27th, and it's free, but you have to register. (That's why I've been rereading this stuff recently).

Karen