On Wed, 10 Dec 2008 10:03:29 -0500, Peter Flom <peterflomconsulting@MINDSPRING.COM> wrote:

>You will probably want to look into Zero Inflated Poisson (ZIP) and Zero Inflated Negative Binomial (ZINB) models. > >DAle has discussed how to program these in NLMIXED, here on SAS-L; a number of authors have written about them. IIRC, J. Scott Long's book "Regression models for categorical and limited dependent variables" has a particularly good section on these. > >Essentially, you run two models: >A) What is the chance of a zero vs. other? >B) Given nonzero count, model count

With a low lambda, you expect many zeroes. Peter offers good advice. I will just add that you may also want to consider the hurdle versions of those zero-inflated analyses, too.

The archives are your best friend at the moment :)

HTH,

Kevin