Power limbo [Power / Sample Size]

posted by Helmut Homepage – Vienna, Austria, 2021-02-19 13:37 (498 d 02:25 ago) – Posting: # 22216
Views: 1,553

Hi ElMaestro,

» Yes to 0.53.

Shit, expected that.

» The risk is up to you or your client.

Such a case is not uncommon. Say, you have single dose studies (highest strength, fasting/fed), multiple dose studies with two strengths (fasting/fed). Then you get the n = 6 of my example.
If you want a certain overall power, then each study has to be powered to \(p_i=\sqrt[n]{p_\textrm{overall}}\).
With n = 6, for 80% → 96.35% and for 90% → 98.26%. Will an IEC accept that?*

» I think there is no general awareness, but my real worry is the type I error, as I have indicated elsewhere.

I know. ;-)

» Related issue, the one that worries me more:
» You test one formulation, it fails on the 90% CI, you develop a new formulation, it passes on the 90% CI. What is the type I error?

I’m not concerned about a new formulation. The first one went to the waste bin → zero consumer risk. The study supporting the new formulation stands on its own. Hence, TIE ≤0.05.

» Well, strictly speaking that would be inflated. But noone seems to give a damn. :-D

I’m indeed concerned about repeating the study (same formulation) with more subjects. Then you get an inflated TIE for sure. Regulators don’t care. They trust in the second study more because it is larger and thus the result ‘more reliable’, I guess.

We have that everywhere. A value in the post-study exam is clinically significant out of range. Follow-up initiated and now all is good. Did the value really improve? There is always inaccuracy involved. Maybe the first one was correct and the second one not.

My doctor gave me six months to live,
but when I couldn’t pay the bill
he gave me six months more.
    Walter Matthau




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