overpowering [General Sta­tis­tics]

posted by Helmut Homepage – Vienna, Austria, 2015-11-06 05:03 (3386 d 00:24 ago) – Posting: # 15622
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Hi BE-proff

❝ overpowered study...what do you mean?


Generally we plan studies for 80–90% power π (where the producer’s risk of failing to demonstrate BE of a formulation which is BE: Type II Error, β = 1 – π). If you submit a protocol to the IEC which >90%, they might not accept it. Hence, “overpowered”. Sometimes rich sponsor know that the CV will be lower and/or the T/R is closer to 100% than what they present in the sample size estimation. Pro­tocol approved, study done, low risk of failure. They call it “to be on the safe side”. I call it playing dice with the health of subjects.

Sometimes the minimum sample size given in guidelines will lead to high power anyway. Example – T/R 0.95, 2×2 cross­over, AR 80–125%; CVs which will lead to >90% power:

 n   CV%
12  ≤13.3 
most regulations, Russian “Red Book”
18  ≤16.6  2008 Russian GL
20  ≤17.9  South Africa MR
24  ≤19.8  Brazil, Saudia Arabia (unless justified otherwise)

The chance of a significant treatment effect increases with power.
Imagine: n 134, T/R 0.97, CV 15%. The 90% CI will be 94.12–99.97%. 100% not included, significant treatment effect (p 0.0485), bingo. Is it relevant? Not at all. You can be >99.9999999999999% sure that the true T/R-ratio is not below 80%…

❝ Power over 100%? :confused:


Negative producer’s risk‽

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