Advantages – performance measure [Two-Stage / GS Designs]

posted by Helmut Homepage – Vienna, Austria, 2015-06-06 01:29 (3241 d 02:14 ago) – Posting: # 14921
Views: 17,854

Dear Detlew!

❝ TXH for educating me.


Come on! Didn’t I got the paper from you?

❝ But I wonder why a not fair comparision should guide me. May it be it is the only we have or not. And a known CV would answer all our kwestiones.


Agree. That’s why I wrote

❝ ❝ Such a comparison is not fair but the only one we probably have.


Even 42.

Indeed! In 1979 I had a great evening in Crete (Beer ⇒ Retsina ⇒ Ouzo ⇒ Raki) with Douglas Adams. Inspiring!

❝ ❝ Below some stuff (the adjusted HP is 0.0413, not 0.416 – which is for OF).

❝

❝ I expected that nitpicking :-D.


Sorry.

❝ Mine was from a sparser grid than that what we know now.


I took mine from the Banana splits.

❝ But was too lazy to recalculate (Remember the Mahatma story?).


Sure. Didn’t I send you my sim’s?

❝ Means to me lower f1 is preferrable, higher f2 also.


Yes.

❝ But you can arrive at higher power with higher than necessary sample size. I think this is meant with "overshot". And this isn't preferrable.


Exactly. That’s why they have this ƒs scaling factor in the formula of the ROS.

❝ I will have a look next time. May be Buddha is enlighten me :cool:.


Buddha doesn’t enlighten anybody. Takes years of meditation to reach some degree of self-awareness. Maybe the Holy Spirit or the Flying Spaghetti Monster? :-D

❝ ❝ ... The winner is the symmetric split for my personal favorite n1 ~0.75 of fixed.

❝

❝ I can't follow you here.

❝

❝ May it be that not only old beliefs die hard but also old Vorurteile (prejudices) :-D?


Best only in this particular case. You cured me already!

❝ I don't see an overall better performance of the symmetrical split w.r.t to your explained f1 and f2 with a fixed n1.


I don’t think that there is one.

❝ Sometimes f1 points to preference of Pocock adj., sometimes to preference for HP or OBF (adj. of course to control TIE), sometimes f2 in the same direction or vice versa.


Exactly.

❝ And the n1 ~0.75*n of fixed rule is not applicable if you bear in mind that the preposition of my post was considerably uncertainty about the intra-subject variability or CV.


I missed that!

❝ Of course, if you have some really good guesstimate of the CV your preferred rule is preferred from the preferred (aka initiated) :cool:.


Yep.

❝ BTW: How did you arrive at the histograms of the sample size?


Crude example:
library(Power2Stage)
N <- as.numeric(power.2stage(CV=0.3, alpha=c(0.001, 0.0413), n1=24,
     npct=seq(0.001, 0.999, 0.001), print=FALSE, details=FALSE)$nperc)
hist(N, freq=FALSE)
abline(v=c(median(N), mean(N)), lty=c(1, 3))

❝ Would it be helpful to have an option to obtain the data for such graphics from the functions in Power2Stage?


For novices, why not? Add a parameter hist=TRUE|FALSE and calculate the tight percentiles – regardless what might be already set in the parameter npct.
—
Dif-tor heh smusma 🖖🏼 Довге життя Україна! [image]
Helmut Schütz
[image]

The quality of responses received is directly proportional to the quality of the question asked. 🚮
Science Quotes

Complete thread:

UA Flag
Activity
 Admin contact
22,988 posts in 4,825 threads, 1,656 registered users;
86 visitors (0 registered, 86 guests [including 2 identified bots]).
Forum time: 03:44 CEST (Europe/Vienna)

The whole purpose of education is
to turn mirrors into windows.    Sydney J. Harris

The Bioequivalence and Bioavailability Forum is hosted by
BEBAC Ing. Helmut Schütz
HTML5