Selection of w and w* [Two-Stage / GS Designs]

posted by d_labes  – Berlin, Germany, 2018-04-26 20:02  – Posting: # 18734
Views: 7,417

Dear Helmut,

» ...
» Using the median of n.tot to define the weights from the sim’s was a – maybe too naïve – attempt. Other suggestions? Some regulatory statisticians prefer the first stage in a TSD to be like in a fixed sample design. For some combinations of n1/CV in my grid this will be ≤ the median of n.tot. In other words, I’m not too optimistic but rather too pessimistic. Now what?

As I already said, DUNO really.

» Example: CV 0.1, GMR 0.95, target power 0.80. Fixed sample design’s n 8 (n1 ⇒ 12 acc. to GLs). n.mean and median of n.tot 12 with the default weights (0.5, 0.25). Even the 95% percentile of n.tot is 12.
» :confused:

If you were pesssimistic, so in the spirit of the MCT ist would be wise to choose the second pair of weights with decreased value. Or do I err here ("real" n2 lower than the pessimistic)?
If I'm right, possible values could be:
w=0.999, w*=0.5 (or something like that value)

Or we stay for that extremal case with the standard combination test?

But to state it again: For me it is a mystery how to choose the weights.
But I think it doesn't make so much difference if we are not totally wrong with our choosen weights.
As far as I have seen so far for a small number of examples: The power is influenced only to a "minor" extent. The TIE is controlled, whatsoever weights we choose.

Regards,

Detlew

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