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From |
Laurie Molina <molinalaurie@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Truncated at zero count data with underdispersion |

Date |
Sun, 10 Oct 2010 17:39:23 -0500 |

Hi all, I have a question, i hope somebody can help my. I am modelling count data truncated at zero: The number of cell phones of households with cells phone. The observed data goes from 1 to 9, with mean equals 1.89 and variance 1.14. I have done some underdispersion tests after running a poisson regression with the truncated data and i reject the one sided hypothesis of equidispersion with a p-value of cero. (the predicted values have mean 1.89 with variance equal .51). Regarding the latent variable, i have also availabre the number of cellphones of all the households, i.e. i have the data of the latent variable that goes from 0 to 9. Here the mean equals 1.15 and the variance equals 1.54. I have also done and underdispersion test after running a poisson regresion with all the data and i get underdispersion (the predicted values have mean 1.15 but variance equal .999). I am interested in the truncated regresion because i want to predict the number of cell phones of the HH who have cell phones. I mean, in addition to the data that i am using for this regresion, i have another list of households and i know wheter they have or they dont have a cell phone. But among the HH in that list, who do have a cell phone, i do not know how many of them they have, and i am interested in that. To my understand if i use a poisson regression, given that my data is truncated i will get inconsistent estimates because the conditional expectation will not be correctly specified as an exponential function of xbeta. So i have to use the command: **** ztp depvar indep var **** But if the latent variable is not poisson i will get inconsistent estimates. I know stata has also availabre the zero truncated negative binomial regression, but since i get underdispersion in the latent variable i think the data is not negative binomial distributed so i will still get inconsistent estimates. Does anyone know any stata command that i could use to model zero truncated count data with underdispersion? Thank you all very much in advance. Regards, Laurie. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Truncated at zero count data with underdispersion***From:*Steve Samuels <sjsamuels@gmail.com>

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