Hello, I have a dataset with proportions that vary around a fixed mean, is it possible to use betareg to look at variance in the dispersion parameter while keeping the mean fixed?
I am very new to R but have tried the following: svec<-c(qlogis(mean(data1$scaled)),0,0,0) f<-betareg(scaled~-1 | expt_label + grouped_hpi, data=data1, link.phi="log", control=betareg.control(start=svec)) I understood that y~-1 could be used to give a fixed mean of 0.5 however I get the following error: Error in linkinv(x %*% beta + offset) : Argument eta must be a nonempty numeric vector I think I can work round this by using: svec2<-c(qlogis(mean(data1$scaled)),0,0,0,0,0) f2<-betareg(scaled ~ expt_label + grouped_hpi | expt_label + grouped_hpi, data=data1, + link.phi="log",control=betareg.control(start=svec2)) This appears to work (ie doesn't return errors), but given i know the mean to be fixed I would like to do this in the model (especially as my data set is small) - is this possible? Thanks in advance. -- View this message in context: http://r.789695.n4.nabble.com/betareg-question-keeping-the-mean-fixed-tp3783303p3783303.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
