Bioequivalence and Bioavailability Forum

Dear Alice!

❝ You had writte T/R = 0.95. With BE margins, we can have 0.80<T/R<1.25. So we need to test all T/R ratio with the function? Or maybe I had'nt understand something?

Well that's the expected mean deviation of test from reference of -5% (we are taking about average bioequivalence here). Most people use this value when they have no other information (like point estimates from previous studies, etc.) The new European Guideline on Bioequivalence states that formulations must not differ by more than 5% in their actual (=measured) contents. Power functions are slightly asymetrical in linear scale. At any given sample size and CV, power for T/R 0.95 is lower than for T/R 1.05 - but equal to T/R 0.95^-1.
For our yesterday's example (20 subjects) we get a power of 83.47% at T/R of 0.95 (and 0.95^-1=1.05263…), but 84.32% at 1.05.
When people sloppily talk about ±5% deviation of test from reference, it's therefore common practice to use 0.95 (not 1.05!) in order to get a conservative estimate of the sample size.

You can try the function with any value you want - but you will get
Err: ratio not between margins!
if ≤0.80 or ≥1.25. Play around with the power-function as well. What power do you expect close to the acceptance margins?

❝ Now, I hope I'll find some references for understand how works Owen's Q function (generally, it's not easy for a student to find an access to these references ).

At least Biometrika is not an exotic journal…

Well, D. Labes offered some help already; my contact is behind the icon at the upper left hand corner of all my posts.