[R] random interactions in lme

From: Jacob Michaelson <jjmichael_at_comcast.net>
Date: Mon 25 Apr 2005 - 00:12:10 EST

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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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Mon Apr 25 00:17:44 2005

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