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

posted by Helmut Homepage – Vienna, Austria, 2017-12-28 21:10  – Posting: # 18121
Views: 18,042

Dear Detlew,

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


» 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.


» 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.

Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. ☼
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