Bioequivalence and Bioavailability Forum

Hi VSL,

❝ It has been seen that In protocol, larger sample size is selected to just pass the study without any scientific justification or selecting high T/R in sample size calculation. Therefore, in many cases, post hoc power is more than 100% or nearly 100%. It is like forced bio-equivalence.

❝ Does regulator seek justification for this?

Power > 100% is a stretch But I know what you mean - power is higher than it would perhaps need to be if you are content with e.g. the usual 80% or 90%. The study will likely pass if you have good control over the T/R. Power is the applicant's problem, usually. It is difficult to argue on basis of ethics and science that 85% power is OK while 95% power is not, or the other way around. And so forth.
You'll see that some companies do not feel extremely confident their true T/R is e.g. 0.95; it is the true T/R that determines power together with variability, yet true T/R is never known. Thus, there is a point in sometimes having a seemingly high samnple size when you are not totally in the driver's seat re. the T/R. And when the trial passes with flying colours and a T/R close to 1.0 then it looks like the trial was over-powered and in hindsight you're thinking sample size was way too high. But you didn't know that in advance, and therefore such a posthoc power consideration can be unjustified.
Remember that even after the trial the true T/R is not known.