[R-sig-eco] ICC confidence intervals and power analysis for random effects in lmer?

[Mollie Brooks]

Hi Brad,
I'm also interested in getting reliable CI on random effects because I want to know how the within treatment variability differs among treatments. The only ways I know to get CI on random effects are to either do likelihood profiling, or (preferably) MCMC sampling. If your desired distribution and link function are built into either glmmADMB or MCMCglmm, then go for those. I have been using ADMB via R2admb recently to do my own profiling and MCMC sampling of semi-non-standard GLMMs. I could try to be more specific and helpful if you have a more specific model formulation in mind, but other people might have better ideas, especially if you wrote to the mixed models list.
best,
Mollie

Mollie Brooks
Ph.D. Candidate
NSF IGERT Fellow
Biology Department
University of Florida
mbrooks at ufl.edu
http://people.biology.ufl.edu/mbrooks




On 11 Apr 2012, at 9:50 PM, Bradley Carlson wrote:

> I'm performing an analysis of behavioral variation among individual
> tadpoles, using individual ID as a random effect and time as a continuous
> fixed covariate in the lmer function in lmer4 package. I'm really
> interested in making inferences about the random effect (i.e. the extent of
> variation among individuals). I'd like to do two things that I can't seem
> to find straightforward answers about and I'm hoping someone can help or
> point me to a good resource.
> 
> 1) The intraclass correlation coefficient is of particular interest to me,
> as it describes the proportion of variation that occurs among individuals.
> Ideally I'd like to report a confidence interval of the ICC but I can't
> find any way to calculate one, other than a function in the psychometric
> package that appears to only work when there are no covariates in the model
> (random effect only).
> 
> 2) A reviewer requested a power analysis of the ability to detect a
> significant random effect. Any tips on how to approach that?
> 
> Thanks for any help,
> 
> Brad
> 
> -- 
> 
> Bradley Evan Carlson
> PhD Candidate
> Intercollege Graduate Degree Program in Ecology
> The Pennsylvania State University
> University Park, PA 16802
> 
> Email: carbrae at gmail.com
> http://homes.bio.psu.edu/people/faculty/langkilde/index_files/carlson.htm
> https://sites.google.com/site/bradleyecarlson/home
> 
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