[R-sig-ME] Sample size and mixed models

Robert Kushler kushler at oakland.edu
Fri Dec 12 15:21:15 CET 2008

I would argue that the larger value (individuals) is always more appropriate
than the smaller value (clusters).  However, the more important issue is
that the "ungrouped" version of the likelihood should be used for these
calculations.  Using the "grouped data" likelihood omits the within cluster
variation and inflates the estimate of predictive power.

Regards,   Rob Kushler

Ben Zuckerberg wrote:
> A very quick (and possibly silly) question for mixed modelers.  Certain 
> metrics such as Nagelkerke's R2 and the sample size adjusted AICc 
> require the user to specify the sample size.  What is the appropriate 
> sample size to use in a mixed model where you might have hundreds of 
> repeat samples on a smaller sample of sites (in this case, the sites are 
> treated as the random factor)?  In my case, the lmer output will produce 
> the following information: Number of obs: 10091, groups: ID, 444.  For 
> calculating sample size adjusted statistics, would you use an effective 
> sample size of 444?  Thank you.
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