On 1/18/07, w jj <[EMAIL PROTECTED]> wrote: > I have a question about the function lme() in R. > > I have a 2*2*3 layout with some missing data (labelled as *). These 3 > factors are labelled as A,B,C, the response is Score. The layout is as > follows:- > > A B C Score > 1 1 1 5 > 1 1 2 * > 1 1 3 1 > 1 2 1 4 > 1 2 2 4 > 1 2 3 * > 2 1 1 3 > 2 1 2 * > 2 1 3 4 > 2 2 1 2 > 2 2 2 * > 2 2 3 5 > > Suppose these data are stored in a data frame called "test". > > If all these 3 factors are fixed, then I can fit a model without the 3-way > interaction as:- > fit1<-lm(Score~A*B+A*C+B*C,data=test) > > If one of these factors, say A, is a random effect variable, then I need to > fit a mixed effect model using lme(). I have read the R documention on > lme(), but I am still not clear how to specify the random argument. I tried > to do:-
You could do it but you don't really want to try to fit a model with several random effects generated by a factor with only two levels. Estimating variances, which is what is done for a random effect, is more difficult than estimating means or other linear combinations of the responses, which is what fixed effects parameters end up being expressed as. Trying to estimate a variance when observing a factor at only two levels is overly optimistic. Just for the record, the call to lmer in the lme4 package would be fit2 <- lmer(Score ~ B*C+(1|A/B)+(1|C:A), data = test) > fit2<-lme(Score~A*B+A*C+B*C,data=test,random=~A, na.action=na.pass) I don't think you want to use na.pass here. The underlying C code for fitting lme or lmer models doesn't take kindly to finding NA's in the data. > > but the system give a message as follows:- > Error in getGroups.data.frame(dataMix, groups) : > Invalid formula for groups > > So how should I specify the arguments? > > Thank you very much for your help! > > Jiajie > > > > ______________________________________________ > R-help@stat.math.ethz.ch 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. > > > ______________________________________________ R-help@stat.math.ethz.ch 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.