Bioequivalence and Bioavailability Forum

Hi Helmut and all,

this looks to me like an ugly work-around rather than a solution.
I am not a WNL user but I'd like to understand why that type of coding fixes it. I believe WNL will fit this model via REML, and on basis of the syntax I imagine this means a covariance matrix with two squared sigmas on the diagonal and zero elsewhere. But to get through to the 'correct' CI there must be a step for derivation of the denominator DF which happens to coincide with the DF you get via the Welch correction when just doing ordinary unpaired t-test with unequal variances. Perhaps that's similar to the SATT option in SAS (which I also don't use). Could be checked?

So, what is really going on within WNL when that weird coding principle is applied - Why does it give the seemingly right result? Anyone knows?