[R] Syntax for lme function to model random factors and interactions

[i_like_macs]

Hello Joshua,

Many thanks for your help, especially from a fellow Bruin (I went there as
an undergrad!). 

I understand that there is another forum for mixed models. If my problem
can't be solved within this thread, I'll have to go there. I do understand
some theory about mixed models, but obviously am far from an expert.

My question is not so much statistical advice, as it concerns the correct
syntax to include random factors and interactions (which include these
random factors) for the lme function. Maybe it's because I'm used to SPSS,
but I find R very difficult to use, even after looking up its built-in help.

I could run your neat code suggestion:

lme(Y ~ (A + B + C + D)^3, data = myData, random = ~ 1 | C, method = "ML") 

but would like to know how to also include "D" as a random factor. My
understanding is that the "random" argument for the lme function is coded
as:

~ x1 + ... + xn | g1 / ... / gm

where the left side describes the model for random effects, and the right
side describes the grouping structure. Reading other posts, I learned that I
need both sides for the code to run without errors. However, it's not clear
to me what both sides represent. The left side appears to be where the
random factors are specified, perhaps like this:

random = ~ C + D

But then this results in errors. Does this mean I have to somehow join the
two following lines of code to specify both random factors?

random = ~ 1 | C
random = ~ 1 | D

It's not clear what the "~ 1" represents here, as I would have guessed that
this is where the random factors would be specified. Is this related to an
intercept-only model?

I'm sorry for sounding so lost. This is because I am. Perhaps I need to know
more theory of mixed models, but this seems to be possible only if I
understand what parts of the lme function are.

Thank you very much again,

Daisuke


--
View this message in context: http://r.789695.n4.nabble.com/Syntax-for-lme-function-to-model-random-factors-and-interactions-tp4630744p4630789.html
Sent from the R help mailing list archive at Nabble.com.