Thank you for your response. The single response/observer most probably explains the complaints that lmer was giving for my example. Maybe this small modification provides a better example and corrects a more serious error in my previous post:
library(lme4) y<-rnorm(30) cond <- rep(gl(3,5,15), 2) obs<-rep(gl(15,1), 2) subj<-rep(gl(5,1,15), 2) dd<-data.frame(y=y,cond=cond,obs=obs,subj=subj) l1 <- lmer(y~cond + (1|cond:obs), data=dd) l2 <- lmer(y~cond + (1|cond:subj), data=dd) l3 <- lmer(y~cond + (1|obs), dd) Understanding the notation is often about 99% of the job, and it is very helpful to see multiple ways to accomplish the same thing. > Douglas Bates a écrit: > I prefer to have a grouping factor constructed with unique levels for > each distinct unit. The only reason I mention constructions like > Treatment:Rat in the original part of this thread is that data are > often provided in that form. > > Reusing "subject" labels within another group is awkward and can be > error prone. One of the data sets I examine in the MlmSoftRev > vignette of the mlmRev package is called Exam and has student > identifiers within schools. The student identifiers are not unique > but the school:student combination should be. It isn't. These data > have been analyzed in scores of books and articles and apparently none > of the other authors bothered to check this. There are some > interesting ramifications such as some of the schools that are > classified as mixed-sex schools are likely single-sex schools because > the only student of one of the sexes in that school is apparently > mislabelled. > > BTW, in your example you have only one observation per level of 'obs' > so you can't use obs as a grouping factor as this variance component > would be completely confounded with the per-observation noise. > >> >> Douglas Bates a écrit: >> >> The difference between models like >> lmer(Glycogen~Treatment+(1|Rat)+(1|Rat:Liver)) >> and >> lmer(Glycogen~Treatment+(1|Treatment:Rat)+(1|Treatment:Rat:Liver)) >> >> is more about the meaning of the levels of "Rat" than about the >> meaning of "Treatment". As I understood it there are three different >> rats labelled 1. There is a rat 1 on treatment 1 and a rat 1 on >> treatment 2 and a rat 1 on treatment 3. Thus the levels of Rat do not >> designate the "experimental unit", it is the levels of Treatment:Rat >> that do this. >> >> -- >> Ken Knoblauch >> Inserm U371 >> Cerveau et Vision >> Dept. of Cognitive Neuroscience >> 18 avenue du Doyen Lépine >> 69500 Bron >> France >> tel: +33 (0)4 72 91 34 77 >> fax: +33 (0)4 72 91 34 61 >> portable: +33 (0)6 84 10 64 10 >> http://www.lyon.inserm.fr/371/ >> >> > -- Ken Knoblauch Inserm U371 Cerveau et Vision Dept. of Cognitive Neuroscience 18 avenue du Doyen Lépine 69500 Bron France tel: +33 (0)4 72 91 34 77 fax: +33 (0)4 72 91 34 61 portable: +33 (0)6 84 10 64 10 http://www.lyon.inserm.fr/371/ ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
