I want to fit a negative binomial model for my count data. I am wondering what the differences for the computation of these three PROCs are in SAS.
There are many overlapping procedures in SAS. If all you want to do is fit a negative binomial model, any of those should be fine. Differences arise in that each of those procedures has additional abilities. For example,
If a procedure does everything you want, there is probably little reason to use a different one. However if it does not or it is difficult, there may be. For example