## Desperate reader [Regulatives / Guidelines]

Hi Hötzi,

» We need the bloody confidence interval.
» As long as we can’t get the standard error of the treatment difference and its associated degrees of freedom, we are at a loss.

If we look at SAS documentation e.g. here and here, then
1. I do not understand the underlying math (just try and look into the spectral decomposition things mentioned as part of DDFM derivation; it sends my head spinning).
2. Whatever SAS does, it seems to require that we work in V through ZGZt+R in order to estimate CI's for the fixed effects.
It would be interesting to see someone who has solid understanding of matrix theory and stats to work out the equations when the between and within-variability for T cannot be separated.
However, since FDA now threw the mixed model out for semi-replicate designs, interesting may in reality just mean academically attractive but possible not too useful at this moment. But who knows - until someone does it and explores it, it is not known if there is an advantageous property hidden somewhere.

Pass or fail!
ElMaestro