I prefer to play it safe [Power / Sample Size]

posted by Helmut Homepage – Vienna, Austria, 2017-12-28 22:10 (1064 d 05:29 ago) – Posting: # 18121
Views: 27,312

Dear Detlew,

» "Normal" is a question one could debate for hours, probably ending in a flame war :-D.

:lol3:

» For me 0.95 or 1/0.95 is as "normal" like setting alpha = 0.05.

Not for me. The former is an assumption whereas the latter fixed by the authority.

» It's a convention to be used if nothing specific about the GMR is known. Nothing more.

Agree.

» And it seemed mostly to work over the years I have observed the use of this setting.
» Of course it is not a natural constant.

Agree again.

» » ... but IMHO, optimistic even if you measure a content of 100% for both T and R. Given that power is most sensitive to the GMR I question the usefulness of 0.95.
»
» Any other suggestion instead of 0.95 :confused:

Communication with the analytical staff & common sense. :smoke:
The GL tells us that the T- and R-batches should not differ more than 5% in their contents. I’m too lazy to browse through my protocols but IIRC, on the average it was 2–3%. Now add the analytical (in)accuracy and – conservatively assuming that the error may be on opposite sides – you easily end up with a GMR worse than 0.95.
Measuring content is not always trivial. Some MR-products are difficult and most topical products a nightmare. Extracting a lipophilic drug from a cream full of emul­sifiers is  great fun  a mess.
If I have to deal with a simple IR-product, the analytical method is very good, and the difference small I’m fine with 0.95 as well.

In general I prefer conservative assumption(s) over optimistic ones. With the former (if they were false) you may have burned money but have a study which passed. With the latter sometimes you have to perform yet another study. Not economic on the long run.

Dif-tor heh smusma 🖖
Helmut Schütz
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