Hi, I'm trying to use nlme to program a model where, as well as a number of fixed effects, I have a random effect for each subject in my model. I would also like to include a correlation statement in my model, where the grouping factor for the correlation is a subset of the observations on a particular subject. However, when I try and program this, R will not let me use a different grouping structure for the random effects and the correlation structure. I can't seem to solve this problem myself and so I would be grateful for any help! Thanks, John Marioni University of Cambridge