On Fri, 15 Sep 2023 01:51:27 +0000 "Sorkin, John" <jsor...@som.umaryland.edu> wrote:
> What is theta, and how does it relate to the parameters of the > negative binomial distribution? Plugging the p (the success probability) and the r (the number of successes until the experiment is stopped) from the Wikipedia article (where they are defined in terms of mean mu and variance sigma^2) together with the variance from ?MASS::rnegbin (where it's defined as mu + mu^2/theta) into Maxima and then solving for theta, I get: solve( [ p = mu / sigma^2, r = mu^2/(sigma^2-mu), sigma^2 = mu + mu^2/theta ], [mu, sigma, theta] ); [ mu = ((1-p)*r)/p, sigma = sqrt(r-p*r)/p, theta = r ] That is, the theta from MASS seems to be equivalent to the number of successes from the formulation in the Wikipedia article. -- Best regards, Ivan ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
