st: negative binomial model

["Mareike" <MareikeHahr@aol.com>]

Dear Statalist,

I want to analyze count data. Given that for several reasons the Poisson
analysis showed to be inappropriate, my idea was to run a negative binomial
model(using the command xtnbreg because I have panel data). But what
happened was that Stata was giving me one iteration after the other (what
appeared in the result window lokked like the following: 
Iteration 14721:log likelihood = -53.558237  (not concave)
and after 3 hours and ten thousands of iterations I stopped the program
without having gotten any result.
Does anybody of you have an idea of what happened? I didn't have the problem
when running the Poisson model using the same dataset.

Thanks for any help

Mareike


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