On Wed, Nov 19, 2008 at 1:37 PM, Eduardo G. Martins <[EMAIL PROTECTED]> wrote: > Dear all,
> I was wondering if someone could help me with the specification of a > formula including both nested and crossed effects in the same model in > lmer. I have one predictor variable, x, and three grouping factors, > a,b and c. Factor b is nested in a but is partially crossed with c. > Also, I'm interested in an interaction between the crossed effects b > and c. I specified a formula in lmer as > y ~ x + (1|a/b) + (1|c) + (1|b:c) > I could fit this model using lmer with no problems but I just would > like to know if that specification is correct. Thank you so much for > any thoughts. That formula describes a model with the characteristics you describe unless the levels of b are implicitly nested. In other words, do the levels of the factor b correspond to different experimental units by themselves or only when considered within a level of a? If different levels correspond to different experimental units, so that there must be more levels of b than of a, then (1|a/b), which expands to (1|a) + (1|a:b), is equivalent to (1|a) + (1|b) and the formula makes sense but I would prefer the more explicit y ~ x + (1|a) + (1|b) + (1|c) + (1|b:c) If the levels of b are only meaningful within levels of a then the term (1|b:c) is not meaningful because b is not meaningful except in conjunction with a. It might help if you explained your experiment in more detail. One message to the group will probably suffice, though. I received 3 copies of your original message. More detail on implicit nesting is available in the part of the slides at http://www.stat.wisc.edu/~bates/UseR2008/WorkshopD.pdf that discuss an analysis of the Pastes data (slides 43 to 56). ______________________________________________ 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.
