[R] random interactions in lme

[Jacob Michaelson]

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