Bioequivalence and Bioavailability Forum

Hi HS,

❝ Do you think that they know/understand the context of Pocock’s original 0.0294 (superiority testing, parallel groups, fixed total sample size k, normal distribution – Z, known and equal σ², interim look at k/2)?

Very good point and I like what you are hinting at.
Defaulting to 0.0294 whenever the word "two-stage" pops up is an understandable thing to do today although I'd like to see that change tomorrow. In the absence of more papers discussing the two-stage designs I can't imagine the change will happen quickly.
I guess I will store it mentally along with the likes of 2.9979×10⁸ m/s and 6.626×10^-34 Js, and I will call it "P_t" for 'Pocock's universial two-stage constant'. Communication and education is necessary.

Let N₁ be the number of subjects in stage 1, let a₁, a₂ be the two alphas and E the overall type I error rate, let CV be the coefficient of variation and T:R the test:ref ratio.
Then:

• For the two meffuds B and C, can we produce proof that E is a function of (or varies with / is not a constant of) a₁, a₂, N₁, CV, T:R?
  
• If the answer is yes, can we prove that substituting a₁ for P_t in method B does not ensure that E stays below 0.05 universally?

Elementary my dear Watson, the answers are given by Potvin herself.

Furthermore, the crackpot paper demonstrated that given for any set of (a₁, N₁, CV, T:R) we can identify an a₂ which keeps E under 0.05 or whatever level is deemed useful.

Hey, next time they call from IQPC or Informa I will suggest such a talk in an upcoming conference.

❝ (...) the topic in one thirds of the chats I had in the coffee-breaks of this week’s workshop in Budapest.

I can imagine. Coffee breaks don't get better than that.