Dear R-help, The negative binomial distribution has several different parameterisations, but I can't seem to figure out what the exact one used in mgcv's negbin family is? negbin() requires a theta argument, but its not clear anywhere in the documentation (that I can find), how this parameter should be interpreted - for example, can it be less than 1? Best wishes, MArk
On 13/11/2013 09:38, Mark Payne wrote:> Dear R-help, > > The negative binomial distribution has several different > parameterisations, but I can't seem to figure out what the exact one > used in mgcv's negbin family is? negbin() requires a theta argument, > but its not clear anywhere in the documentation (that I can find), how > this parameter should be interpreted - for example, can it be less > than 1?I believe it is the same as MASS (the package) explained in MASS (the book). As its help says ....> > Best wishes, > > MArk >-- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
var(y) = mu + mu^2/theta where E(y) = mu. best, Simon On 13/11/13 10:38, Mark Payne wrote:> Dear R-help, > > The negative binomial distribution has several different > parameterisations, but I can't seem to figure out what the exact one > used in mgcv's negbin family is? negbin() requires a theta argument, > but its not clear anywhere in the documentation (that I can find), how > this parameter should be interpreted - for example, can it be less > than 1? > > Best wishes, > > MArk > > ______________________________________________ > R-help at r-project.org mailing list > 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. >-- Simon Wood, Mathematical Science, University of Bath BA2 7AY UK +44 (0)1225 386603 http://people.bath.ac.uk/sw283