Using lme() for split plot
Thanks for the tip. That lead me to find this paper: http://www.ualberta.ca/~baayen/publications/baayenDavidsonBates.pdf which looks like it will answer my problem. Depending on how we actually decide to execute the test it might turn out to be nested like those other examples, but it's nice to have options. Thanks again.
On Thu, May 7, 2009 at 6:13 PM, Bert Gunter <gunter.berton at gene.com> wrote:
Crossed Random effects are difficult using lme (wasn't designed for it). Try lmer in the lme4 package if you need this. Bert Gunter Genentech Nonclinical Biostatistics -----Original Message----- From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Joshua Stults Sent: Thursday, May 07, 2009 3:02 PM To: Rub?n Roa-Ureta; r-help at r-project.org Subject: Re: [R] 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
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Joshua Stults Website: http://j-stults.blogspot.com