GMR = fixed! [Two-Stage / GS Designs]

posted by Helmut Homepage – Vienna, Austria, 2017-02-18 16:23  – Posting: # 17085
Views: 10,809

Hi BE-proff,

» What do you mean under controlled GMR […]

Let me answer for our ol’ Capt’n: The GMR in the estimation of interim power (stage 1) and in the sample size estimation for the second stage is fixed (and not the observed one).

» - being within 0.95-1.05? Correct? ;-)

Nope. The observed one can be anything. For Potvin’s B and C it is 0.95 (or 1/0.95 if you prefer). Other methods use other fixed GMRs (the A in my figures below). Look them up in the publications (AFAIK, only methods with 0.95 and 0.90 are published).

» So, if 1 stage of any method shows GMR 1.19 which figure shoud be taken for 2 stage: 0.95 or 1.19 :confused:

For most methods 0.95. If you already expect a “bad” GMR, you could opt for Montague’s or one of Anders’ methods which use a fixed GMR of 0.90 (or 1/0.90). Alternatively you could work with one of the methods with a futility criterion (stopping in stage 1).
Only fully adaptive methods (e.g., by Karalis and Macheras) would use the observed GMR 1.19. See my paper mentioned below why this might not be a good idea…*

Dif-tor heh smusma 🖖
Helmut Schütz

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