[R] Negative Binomial: Simulation

Hadassa Brunschwig dassybr at gmail.com
Fri Jul 14 15:18:34 CEST 2006

Addition to last email:

The problem basically arises also when I want to calculate (plot) the
cumulative distribution of the negative binomial with the calculated
parameters mu and theta!

On 7/14/06, Hadassa Brunschwig <dassybr at gmail.com> wrote:
> Hi R-Users!
> (sorry about the last email)
> I fitted a negative binomial distribution to my count data using the
> function glm.nb() and obtained the calculated parameters
> theta (dispersion) and mu.
> I would like to simulate values from this negative binomial distribution.
> Looking at the function rnbinom() I was looking at the relationship
> between the two possible parametrizations of the negative binomial and found
> that for this fuction I must use:
> prob = theta/(theta+mu)     and       size = theta
> Theta, however, is not an integer. So how can size (which is the number of
> successes) equal theta?
> I know there is a function rnegbin which does what I want. I would still
> like to raise the above question (probably a more statistical one
> than R).
> Thanks a lot for any comments.
> Hadassa

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