Sarah sent this directly to me and I am pretty much wiped out right now having finished the third short course in a month and preparing or helping to prepare three other presentations. Could someone else take a stab at answering this? I'm tired and I have a full day of international travel ahead of me tomorrow and I would probably give nonsense advice. It looks as if it is urgent for her.
On Thu, Jul 23, 2009 at 11:28 AM, <s.buckmaster.08 at aberdeen.ac.uk> wrote:
I am an MSc Ecology student in Scotland, UK and am struggling to analyse my dissertation data in R - I only have today and tomorrow to understand my output and so was hoping you could offer some advice. I would be really grateful! I carried out a plant experiment examining plant interactions between two species (A and B) under different watering treatments. I had - 7 watering treatments (7 different watering frequencies labelled 1-7) ...and... - 3 replicates of each treatment At each watering treatment, I had 5 different combinations of plants. I have shown how I have labelled these in brackets for species A: A in isolation (Aiso) A+A monoculture (Amono) A+B interspecific competition (Amix) .. and the same for species B. The first step is to check species A for interspecific competition.... I need to see whether I have a significant replicate effect (block effect) and as this will be a random effect, I am going to use a lme. I have the following factors: Response variable: ?Amix Random effect: ? ? ?Block (replicates labelled as 1,2,3) Main effect: ? ? ? ? ?watering treatment (wt) (1-7) Covariate: ? ? ? ? ? ? Aiso Covariate: ? ? ? ? ? ? Amix.initialsize (initial biomass of Amix to account for any size variation before treatment was started) I used following formula in lm (before I thought I'd have to include block as random effect): lm1<-lm(Amix~Aiso+wt+block+Amix.initialsize+Aiso:wt) but do not know how to structure it in an lme. How would I do this? Also, what is the difference between an lme and an lmer as I was unsure which one to use, Thank you, Sarah Buckmaster E-mail: s.buckmaster.08 at aberdeen.ac.uk