[R-sig-ME] random effects models with small n

Felix Bach Felix_Bach at gmx.de
Fri Jun 17 13:08:10 CEST 2011

Dear all,

I recently saw an article in which the authorsperformed a random effects analysis with lme4  which used a group (2 levels)x condition (3 levels) x effect (4 levels) and ratio (10 levels) as fixed factors and subject as random factor. Sample size was 16 animals. They used MCMC estimation and obtained p-values of 0.0001 (lets ignore the use of p values in a Bayesian framework). How reliable are those estimates? I can't imagine that you can reliable are p-values (or credibility intervals) with such a complex models and a sample size of 16? If the model assumption of an exchangable covariance structure is valid, could you trust the results? 
Best wishes, Felix


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