Hi All,
I'm taking an Experimental Design course this semester, and have spent
many long hours trying to coax the professor's SAS examples into
something that will work in R (I'd prefer that the things I learn not
be tied to a license). It's been a long semester in that regard.
One thing that has really frustrated me is that lme has an extremely
counterintuitive way for specifying random terms. I can usually figure
out how to express a single random term, but if there are multiple
terms or random interactions, the documentation available just doesn't
hold up.
Here's an example: a split block (strip plot) design evaluated in SAS
with PROC MIXED (an excerpt of the model and random statements):
model DryMatter = Compacting|Variety / outp = residuals ddfm =
satterthwaite;
random Rep Rep*Compacting Rep*Variety;
Now the fixed part of that model is easy enough in lme:
"DryMatter~Compacting*Variety"
But I can't find anything that adequately explains how to simply add
the random terms to the model, ie "rep + rep:compacting + rep:variety";
anything to do with random terms in lme seems to go off about grouping
factors, which just isn't intuitive for me.
Any help?
Thanks in advance!
--Jake Michaelson