On Sun, 2006-10-29 at 11:06 -0800, Spencer Graves wrote: > I can think of two ways to get confidence intervals on intraclass > correlations (ICCs) and more accurate intervals for variance > components: (1) modifying 'simulate.lme' to store the estimated > variance components as well as "logLik" and (2) using 'lmer' and > 'mcmcsamp' in library(lme4). > > The difficulty with (1) is that you have to make a local copy of > 'simulate.lme', then figure out where and how to modify it. I've just > looked at the code, and it looks like the required modifications should > be fairly straightforward. The problem with (2) is that you would have > to learn the syntax for a nested model for 'lmer'. It's different from > that for 'lme' but not difficult. The 'lmer' function is newer and > better in many ways but is not as well documented and does not have as > many helper functions yet. The best documentation available for it may > be the 'MlmSoftRev' vignette in the 'mlmRev' package plus the "R News > 5/1" article from May 2005. If you are not familiar with vignettes, > RSiteSearch("graves vignette") produced 74 hits for me just now. Find > 'vignette' in the first hit led me to an earlier description of vignettes. > > If it were my problem, I'd probably try the second, though I might > try both and compare. If you try them both, I'd be interested in the > comparison. If the answers were substantially different, I'd worry. > > Hope this helps. > Spencer Graves >
I'm familiar with making nested models in lmer but I'm not familiar with mcmcsamp but will check it out. Thanks. I used nlme/lme because it has the intervals function while (at least the last time I checked), lme4/lmer did not. The way I've done the bootstrapping (sampling at each level) sounds the same as using a simulation. But articles and references I've found indicate that only the highest level (a if c is nested in b and b is nested a) should be sampled. Rick B. -- Richard A. Bilonick, Ph.D. Assistant Professor University of Pittsburgh School of Medicine Department of Ophthalmology 412 648 9138 BST S 207 ______________________________________________ R-help@stat.math.ethz.ch 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.