Using lme() for split plot

That's a good example with a couple levels of nesting (similar to the
examples in the other book), but they still only have one factor,
'Variety', nested in each block. ?Am I missing something? ?Should I
make up a psuedofactor with four levels to code my two two-level
factors?


On Thu, May 7, 2009 at 5:46 PM, Rub?n Roa-Ureta <rroa at udec.cl> wrote:

Joshua Stults wrote:

Hi,

I'm trying to figure out how to use lme() for analyzing a split-plot
experiment. ?I've been looking at the examples from the 'R Book',
those are nested but with only one factor at the whole-plot level, my
test is 2^2 at the whole-plot level, with a single many level factor
at the sub-plot level. ?My question is about properly specifying the
random effects part of the model,

lme( y ~ block + a*b*poly(c, n), random=~ ? )

Where 'a' and 'b' are my two level whole-plot factors and 'c' is the
many level sub-plot factor. ?I'm not sure what to use to get the right
error terms. ?Do I use two error terms:

random = ~ 1 | block/a + 1 | block/b

or one:

random = ~ 1 | block/a*b

or something else entirely? ?I haven't been able to find any relevant
examples on Google. Thanks for any suggestions/pointers.

Have you checked Pinheiro and Bates 2004 Mixed-effects models in S and
S-PLUS? They have a split-plot example starting on p. 45.
Rub?n

--
Joshua Stults
Website: http://j-stults.blogspot.com