See this post: http://finzi.psych.upenn.edu/R/Rhelp02a/archive/7144.html
Cheers, Simon. On Mon, 2008-03-17 at 17:04 +1100, Steve Candy wrote: > > Craig A Faulhaber wrote: > > > > >I am interested in using a generalized linear mixed model with data > > > that best fits a beta distribution (i.e., the data is bounded between > > > 0 and 1 but is not binomial). > > .. > > >For clarification, here's what I'm trying to model: > > >I have a beta-distributed response variable (y). I have a fixed-effect > > > >explanatory variable (treatment), and I'd like to include a random term > > > >for individuals used in the experiment. The model in lmer would be: y > > > >~ treatment + (1 | individual). As far as I can tell, the appropriate > > > >link function for the model would be the logit. > > > > If you want to use a GLM you could use the binomial/logit > quasi-likelihood approach for your ratio. Say the ratio is r=n/N then > use binomial n with binomial total N (these do not have to be integers) > but remember to use prior weights of 1/N and estimate the > over-dispersion parameter. If you use the ratio, r, directly with a > binomial total of 1 then the prior weights are simply 1 and can be > ignored. This quasi-likelihood approach for a ratio was given by > Wedderburn (1974) (see McCullagh and Nelder, 1989, Sec 9.2.4). BTW > random effects with a beta distribution included in the linear predictor > via a link function such as the logit can be fitted as a HGLM > (Hierarchical Generalized Linear Model)(Lee and Nelder, 1996, 2001) for > binomial data (i.e. considered binomial conditional on the random > effects). Only the GenStat package is set up to fit HGLMs (as far as I > know). (L & N, 1996, J.R.Statist.Soc B 58, 619-678; L & N 2001 > Biometrika 88, 987-1006). > > > > Hope this helps > > Steve Candy > > > > > ___________________________________________________________________________ > > Australian Antarctic Division - Commonwealth of Australia > IMPORTANT: This transmission is intended for the addressee only. If you are > not the > intended recipient, you are notified that use or dissemination of this > communication is > strictly prohibited by Commonwealth law. If you have received this > transmission in error, > please notify the sender immediately by e-mail or by telephoning +61 3 6232 > 3209 and > DELETE the message. > Visit our web site at http://www.antarctica.gov.au/ > ___________________________________________________________________________ > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@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 Blomberg, BSc (Hons), PhD, MAppStat. Lecturer and Consultant Statistician Faculty of Biological and Chemical Sciences The University of Queensland St. Lucia Queensland 4072 Australia Room 320 Goddard Building (8) T: +61 7 3365 2506 http://www.uq.edu.au/~uqsblomb email: S.Blomberg1_at_uq.edu.au Policies: 1. I will NOT analyse your data for you. 2. Your deadline is your problem. The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. - John Tukey. ______________________________________________ R-help@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.
