[R-sig-ME] Minimum number of levels for mixed model

[nrm2010]

Hello, Ben,


Thank you for the response.  I created some confusion by stating treatment (trt)
instead of the treatment blocks, of which there are 3.
The Murtaugh paper seems to take one position on the perhaps philosophical issue previously
discussed on the forum concerning whether or not the model design has to be faithful
to the experimental design. 
 
My larger question is how often it will be feasible to use mixed models
with nested effects if we require a minimum of  5^n samples for n levels and we try
to be faithful to the experimental design.

Thinking of the adage that all models are wrong and some are useful, how wrong
 are we if the random variable has 3 or 4 levels rather than 5, and how useful are we
if we require 5^n samples?

Thank you for your assistance.

Toby Gass