Thanks Ben. After some investigation it does appear that the the DFs are computed on the fly and not saved. I was able to perform some ad hoc code surgery on summary.merModLmerTest to get it to save and display the DFs. It's not pretty but it will work for now. I will send a note to the package maintainer requesting this.

Jake

> Date: Wed, 20 Nov 2013 17:37:25 -0500
> From: bbolker@gmail.com
> To: r-sig-mixed-models@r-project.org
> Subject: Re: [R-sig-ME] extract DFs from summary.merModLmerTest
> 
> On 13-11-20 05:27 PM, Jake Westfall wrote:
> > I see that package lmerTest will compute approximate degrees of
> > freedom via the Satterthwaite method for test of fixed effects from
> > merMod objects, and it uses these to provide some p-values. Great.
> > But how do I extract the computed Satterthwaite degrees of freedom?
> > They are not displayed in the default output of
> > summary.merModLmerTest objects (which is a big "WTF" in itself, but
> > nevermind), not discussed in the package documentation as far as I
> > can tell, and studying str(summary(fittedModel)) has not given any
> > clues about where they are stored... surely they must be saved
> > somewhere, right??
> > 
> 
>  They don't *have* to be stored (although I agree it would be a good
> idea); they might be computed on the fly and used for computing the
> p-values, or even printed out, but not stored in the summary object.
>   You might have to start digging through
> 
> getMethod("summary","merModLmerTest") and
> lmerTest:::totalAnovaRandLsmeans
> 
> but these are pretty scary pieces of code.  Maybe send a wishlist item
> to the maintainer ... ?
> 
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