[R] Negative Binomial: Simulation

From: Hadassa Brunschwig <dassybr_at_gmail.com>
Date: Fri 14 Jul 2006 - 23:12:52 EST


Hi R-Users!

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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