I am modelling a nested mixed-effects model with just the intercept in the random part, of the form:
fit4<-lme(fixed = Stdquad~factor(LayoutN)+factor(nCHIPS.fixed), random = ~1|Class.Ordered/student)
When trying to check the assumption on the independent, identically distributed (iid) random effects in SPlus using
ranef(), I keep getting the error:
Problem in sort.list: ordering not defined for mode "list": sort.list(x, partial)
I suspect the nesting is the problem since if I remove student, the plots come up fine.
I would like to know how I can check that the random effects are iid and are independent for different groups using S-Plus (or R since its very similar).