sample size in bioequivalence studies [Power / Sample Size]

posted by DavidManteigas – Portugal, 2017-08-03 14:40 (2243 d 15:37 ago) – Posting: # 17651
Views: 18,506

Hi daryazyatina,

For some reason, I can't see the image with the formula that you put on the first post.

❝ For comparison, I use all the standard properties. Design 2x2, confidence intervals 0.8 - 1.25, power 0.8, alpha 0.05.

❝ The only thing about what I'm not sure is CV. Because in formula that I used this is intra-subject variability, but in PowerTOST() this is coefficient of variation as ratio. In calculations in both cases I used СV - 0.3.

Within subject standard deviation and within subject CV are different parameters. Nevertheless, I think that this is not the only reason for such a big difference.

There is a sentence in one of the articles that is quoted on SampleNTOST formula that may clarify this issue:

"This formula is less conservative than Formula (5), but it may result in a lower actual power than the required. For example, when α = 0.05, σ = 0.3, Δ = 0.2, θ = 0.01 and a required power = 0.80, the sample size from Formula (6) [Formula from Chow] is 17 per sequence, but the actual power obtained by this sample size is only 0.69."

So by reading this, I am not sure if Chow formula might be appropriate to calculate sample size for BABE trials. I have just quickly read the article, so I may not be doing a proper analysis. Perhaps dlabes might clarify this, since he is the master that we all should thank for the amazing PowerTOST package :-D

Complete thread:

UA Flag
 Admin contact
22,759 posts in 4,775 threads, 1,627 registered users;
19 visitors (0 registered, 19 guests [including 11 identified bots]).
Forum time: 06:17 CEST (Europe/Vienna)

In God we trust;
all others must bring data.    W. Edwards Deming

The Bioequivalence and Bioavailability Forum is hosted by
BEBAC Ing. Helmut Schütz