st: Zero Trunctated and One inflated Poisson

[Giorgio Ricchiuti <g.ricchiuti@tiscali.it>]

Dear All,
I have been modelling the number of affiliates that the firm i has in 
the country j. My data are zero-truncated but unfortunately are even 
one-inflated (75% of cases). I did not find any possibility to analyse 
this mix-model in STATA 9.0 (neither using for example zip or ztp). I 
worked out the maximum likelihood, and I changed the adofile of zip as 
follows:



           mlsum `lnf' = cond($ML_y1 == 1 ,

                       ln(1/(1+exp(-`zg')) + 
1/(1+exp(`zg'))*exp(-exp(`xb'))),

                       ln(1/(1+exp(`zg'))) - 2*exp(`xb') + `xb'*$ML_y1 -

                                  lngamma($ML_y1+1) ) ;



Of course I also changed gradient and hessian but, unfortunately, I am 
not a developer, hence I did some mistake.

Does anyone help me, explaining either how to change the maximum 
likelihood correctly or developing the model directly in Stata?

Thanks a lot

Giorgio

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