Syntax for lme function to model random factors and interactions
Inline:
On 2012-05-21 11:17, i_like_macs wrote:
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.
Just a small comment, since you're interested in correct syntax: you apparently consider A*B to represent the (A,B) interaction term; in R, it's A:B and this *is* clearly documented in the help pages. Peter Ehlers
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.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.