[R-sig-ME] Presenting results of a mixed model containing factors

[Ben Bolker]

Sarah Dryhurst <s.dryhurst at ...> writes:

> 
> Hi Ben,
> 
> Thank you for your reply!  I don't really want to calculate the main
> effects as it doesn't make much biological sense (to me!).  I just
> wasn't sure whether this was "required" in terms of statistical
> reporting.  That interaction effect is what I am interested in
> largely, as it's the combined effect of the different treatments that
> is my focus.

  I think it would still be worth reporting the main effects, as
their size puts the size of the interaction in perspective (e.g. I
would generally like to be able to judge the size of the interaction
*relative to* the main effects, not just its magnitude/t statistic/
p value ...

> 
> With regards to the lack of variance at the Block level, would you
> recommend dropping this level here?  It doesn't seem to make too much
> sense to keep it there...

  Doesn't matter too much, since the results will be almost identical.
May be worth checking without, to double-check that the zero-variance
result hasn't thrown off the optimization, but I would personally
probably err on the side of reporting it (or say that it was in 
the original model but estimated as being effectively zero).