st: Poisson regression -not concave-

[Paolina Medina <carmencitamedina@gmail.com>]

Stata listers,

I'm trying to run a poisson regression model in which the dependent
variable is the number of mobile phones from the households, and among
other explanatory variables i am using a dummy wariables which takes
the value of 1 when the household has at least one cell phone and zero
otherwise.

But it turns out that whenever i use that dummy variable the iterative
process in stata does not converge, and it can be read for example:
iteration 380: log likelihood = -7734.6891  (not concave)

It i drop that dummy variable i get convergen at Iteration 3:   log
likelihood = -7734.6927

Does anyone has any suggestion or explanation?
And where can i get more information about the numerical process
behind the maximum likelihood estimation?

Thank you very much in advance.

PM
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