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Re: st: Re: pprob

From   Philip Ender <>
Subject   Re: st: Re: pprob
Date   Sat, 2 Oct 2010 08:23:46 -0700

Stephen Sullivan <> wrote:

Could someone please provide some Stata advice with respect to "pprob"?
I have a dataset, which does not appear to fit the Poisson distribution.
I then ran glm and nbreg commands as suggested
To see how the my variable fit the Poisson and negative binomial
distributions, I downloaded and used the nbvargr command.
Nevertheless, something seems strange as all pprob values for the Poisson are 0.

The mean value for your data is 47.92857 so the poisson probabilities
for small counts (0 to 11) is smaller than the number of decimal
places in the output.  The -nbvargr- program works best with
relatively small mean counts that are encountered in classroom data.
You can try increasing the n() option to 55 or you can subtract a
constant from each of the observations for graphing purposes.   Sorry
that you had problems with the program.

Phil Ender
UCLA Statistical Consulting Group
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