Data for 2nd stage of Potvin’s designs [Two-Stage / GS Designs]
Hi BEproff,
All calculation of sample size requires that CV and GMR be plugged in. You have a choice between using the observed GMR or a fixed GRM like 0.95. There is a lot of confusion about it, but the short version is: Two stage methods in all known forms only behave well if the true GMR is controlled. Therefore methods using GMR=0.95 (Potvin B and C and more) behave well when that criterion is true. Performance easily become abysmally bad if you are not in control of the GMR.
It is in the eye of the beholder. B has a bit lower observed alpha inflation than C. Asking why an authority does prefers C to B, or why an airline passenger prefers beef over chicken, is not productive.
Both use GMR=0.95 regardless of observed GMR.
Yes, all this is bloody confusing and it is easy to take the wrong decisions in this area. If you just remember the sentence in red above and base your decisions on it, you'l be more or less fine.
❝ 1) is it correct that GMR and CV are required for sample size calculation for 2nd stage in all Potvin's designs?
All calculation of sample size requires that CV and GMR be plugged in. You have a choice between using the observed GMR or a fixed GRM like 0.95. There is a lot of confusion about it, but the short version is: Two stage methods in all known forms only behave well if the true GMR is controlled. Therefore methods using GMR=0.95 (Potvin B and C and more) behave well when that criterion is true. Performance easily become abysmally bad if you are not in control of the GMR.
❝ 2) Why Method C is considered "better" for sponsors than Method B?
It is in the eye of the beholder. B has a bit lower observed alpha inflation than C. Asking why an authority does prefers C to B, or why an airline passenger prefers beef over chicken, is not productive.

❝ The 1st question arised because Potvin's article dated 2007 says that only CV is needed for A and B while Method C uses both GMR and CV.
Both use GMR=0.95 regardless of observed GMR.
Yes, all this is bloody confusing and it is easy to take the wrong decisions in this area. If you just remember the sentence in red above and base your decisions on it, you'l be more or less fine.
—
Pass or fail!
ElMaestro
Pass or fail!
ElMaestro
Complete thread:
- Data for 2nd stage of Potvin’s designs BE-proff 2017-02-18 06:40 [Two-Stage / GS Designs]
- Data for 2nd stage of Potvin’s designsElMaestro 2017-02-18 10:20
- Data for 2nd stage of Potvin’s designs BE-proff 2017-02-18 13:29
- GMR = fixed! Helmut 2017-02-18 16:23
- Data for 2nd stage of Potvin’s designs BE-proff 2017-02-18 13:29
- “Type 1” slightly higher power than “Type 2” for the same adj. α Helmut 2017-02-18 11:51
- “Type 1” slightly higher power than “Type 2” for the same adj. α BE-proff 2017-02-18 13:31
- Terminology Helmut 2017-02-18 16:27
- Terminology Yura 2017-02-20 11:28
- Which GMR to plug in ElMaestro 2017-02-20 11:46
- Which GMR to plug in BE-proff 2017-02-21 11:35
- Which GMR to plug in ElMaestro 2017-02-21 11:47
- Which GMR to plug in BE-proff 2017-02-21 11:35
- Validated frameworks; observed GMR not relevant Helmut 2017-02-22 12:03
- Validated frameworks; observed GMR not relevant Silva 2017-03-09 01:26
- GMR, theta 0 and that all d_labes 2017-03-09 09:21
- GMR, theta 0 and that all Silva 2017-03-09 12:38
- GMR, theta 0 and that all ElMaestro 2017-03-09 12:56
- GMR, theta0 and that all d_labes 2017-03-09 13:55
- GMR, theta0 and that all Silva 2017-03-09 18:01
- GMR, theta 0 and that all Silva 2017-03-09 12:38
- GMR, theta 0 and that all d_labes 2017-03-09 09:21
- Validated frameworks; observed GMR not relevant Silva 2017-03-09 01:26
- Which GMR to plug in ElMaestro 2017-02-20 11:46
- Terminology Yura 2017-02-20 11:28
- Terminology Helmut 2017-02-18 16:27
- “Type 1” slightly higher power than “Type 2” for the same adj. α BE-proff 2017-02-21 11:31
- “Type 1” slightly higher power than “Type 2” for the same adj. α BE-proff 2017-02-18 13:31
- Data for 2nd stage of Potvin’s designsElMaestro 2017-02-18 10:20