Bioequivalence and Bioavailability Forum

Hi Astea,

❝ I used to calculate CI in the standard 2x2x2 crossover (I've written macros in excel), but now I have to calculate CI in the Four-period study (2x2x4). Google could not help me to find clear information of how to do this. Can you please point me articles or presentations where there is an exact formula for CI?

I don't think there are exact formulae published.
If you're going for a mixed effects model (for example if you target US FDA) then you definitely need an optimising algorithm.
If you are aiming for EMA (all factors incl. subject as fixed) then you can probably derive exact formulae by some algebraic gymnastics, but they can get complicated if there are imbalances or subjects with a missing period value.