R help - Dec 2003 - question regarding variance components

I am using a two-factor ANOVA model with random factor effects including
the interaction, i.e. the factors are crossed.  I would like to be able to
generate all four variance components along with approximate confidence
intervals using the NLME package.  However, I do not know how to specify
the random option because of two problems.  First, I do not know how to
enter the interaction term into the option.  Second, I do not know how
to enter in the covariance matrix (see Neter et. al., Applied Linear
Statistical Models, 4th ed., page 977).  Is there anyone who has
confronted this problem before that would be willing to help?  Thank you.


Philip Turk

Assuming you are measuring Y and you have factor A fixed and factor B
random, I would create a model like:

mod<-lme(Y ~ A, random=~1|B/A, mydata)
VarCorr(mod1)

the term "random=~1|B" tells the model that B is a random factor,
adding
the "/A" to get "random =~1|B/A" tells the model you want
the
interaction between the fixed and random factors.

VarCorr gives you the variance components of the model.

All is answered much better (and with examples) in Pinheiro and Bates
2000 (it's in the first chapter) and in Crawley 2002.

I have posted a question similar to yours times ago, and got an
excellent reply from Prof Bates; search the archives for it.


If ALL your factors are random try something:

mod<-lme(Y~1,random=~1|A/B, mydata)
VarCorr(mod)

but here I am more guessing than anything. Get Pinheiro and Bates 2000
for this.


Cheers,

Federico


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Federico C. F. Calboli

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