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
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