Re: st: RE: Negative Binomial Models

[Jesper Sorensen <sorensen@mit.edu>]

I haven't read the Maddala, but my impression is that it is not a 
matter of should or should not, but rather that when the expected 
mean is sufficiently high, the poisson and neg binom start to look at 
lot like the normal distribution, and hence you are just as well off 
using OLS etc.  Scott Long has a nice demonstration of this in his 
book on LDVs.  Of course, having a couple of cases with high counts 
doesn't mean that the mean is high.

//Jesper




> Should or should not?
>
> I'd like to hear the grounds for that. I find it
> difficult to believe that any such criterion tenet
> aquam. You should use a negative binomial distribution
> whenever fitted probabilities are close to observed
> probabilities.
>
> The underlying frequencies are not that germane.
> But if the total number of individuals in the sample
> is large, at least some cell frequencies are likely
> to be. In fact, to get a good handle on probabilities
> in the tail, a very large sample is a really good idea.
>
> I'm interested in comments on this. If you type
>
> . ssc type nbfit.hlp
>
> there's a worked example in which the peak frequency
> was 807.
>
> Nick
> n.j.cox@durham.ac.uk
>
> >  -----Original Message-----
> >  From: Nick Cox
> >  Sent: 14 October 2004 00:38
> >  To: 'statalist@hsphsun2.harvard.edu'
> >  Subject: RE: Negative Binomial Models
> >
> >
> >
> >
> >  Nick
> >  n.j.cox@durham.ac.uk
> >
> >  > -----Original Message-----
> >  > From: owner-statalist@hsphsun2.harvard.edu
> >  > [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of MacDonald,
> >  > John
> >  > Sent: 14 October 2004 00:23
> >  > To: statalist@hsphsun2.harvard.edu
> >  > Subject: st: Negative Binomial Models
> >  >
> >  >
> >  > Is there a maximum number of counts one should not exceed
> >  > when using the negative binomial model?  Even if there is a
> >  > adjustment for exposure (e.g., rate of homicides in a city). 
> >  > I have a data set with over 200 homicides in some cities and
> >  > I saw a reference in an article of American Journal of
> >  > Sociology to Maddala's 1977 econometrics textbook that said
> >  > you should exceed 50 counts.  Is this true?
> >  >
> >  >
> >  >
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