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Re: st: Basic question to Count Data models

From   Maarten buis <>
Subject   Re: st: Basic question to Count Data models
Date   Wed, 27 Feb 2008 17:52:41 +0000 (GMT)

--- Markus Köller <> wrote:
> I have some basic questions about Count Data Models.
> I am trying to estimate the total number of children a woman gives
> birth to dependend on some explanatory variables, like f.e.
> education_high, education_low and age.
> F.E. Amount of Children= f(educ_high, educ_low, age)
> I want to use a Count Data Model, since Poisson distribution seems to
> be the proper assumption for it.
> Problem: I don´t have any idea how to implement it into stata. Does
> stata have such functions? And what are the commands for them?

-poisson-, you could have found that by typing -findit poisson-, or 
-findit count-
> Another problem: Someone told me that "dispersion" or
> "under-dispersion" might be a problem with a Count Data Model. I did
> some research but couldn´t find anyhting about that. Does anyone of
> you know whether this is true? And if so, can you give me a hint or
> literature suggestion, what "under-dispersion" is and how I could
> face it in my problem?

Yes, that is a known problem. A good place to start learning about
count models and how to perform these analyses in Stata is "Regression
Models for Categorical Dependent Variables Using Stata" by J. Scott
Long and Jeremy Freese:

Hope this helps,

Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

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