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 [[alternative HTML version deleted]]
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
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 >