Hello,

I've recently installed the latest version of lme4, and I'm admiring  
the new hatTrace function. The function notes reference the  
Spiegelhalter et al. 2002 paper, "Bayesian measures of model  
complexity and fit (with discussion)". I'm wondering if anyone knows  
whether the measure returned by this function is equivalent to the  
effective degrees of freedom described by Hodges and Sargent 2001 in  
Biometrika, "Counting degrees of freedom in hierarchical and other  
richly-parameterized models". This measure is used in a further paper  
by Vaida and Blanchard 2005 Biometrika, "Conditional Akaike  
information for mixed-models". If these measures are the same, this  
will allow one to calculate a conditional AIC where the K term is  
estimated using the trace of the hat matrix.

Thanks,

Kyle
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