## Fieller’s (‘fiducial’) confidence interval [General Sta­tis­tics]

Dear ElMaestro,

» For such cases we are setting logscale to False, right?

Correct in so far if we use the approximation that the estimate of µR is (statistically) greater than zero. A very reasonable assumption for the usual metrics AUC and Cmax IMHO.
But this has than nothing to do with Fieller’s (‘fiducial’) confidence interval, a more correct method for deriving a confidence interval for the ratio of untransformed PK metrics.
PowerTOST has for this case the functions
- CI.RatioF() - power.RatioF() - sampleN.RatioF()
Have a look into the man pages of these functions and notice that these functions don't have a logscale argument.

» I will read up on the other stuff. Still not sure how to derive the CI. ...
Eventually the book

Hauschke D, Steinijans VW, Pigeot I.
Bioequivalence Studies in Drug Development
Chichester: John Wiley; 2007

may help.
Especially chapter 10 Equivalence assessment for clinical endpoints.
If you don't own this book, gimme a hint.

Regards,

Detlew