## Two at a Time [Power / Sample Size]

Hi XH7081,

❝ First of all thank you for the wonderful PowerTOST package!

Welcome. THX to Detlew Labes and Benjamin Lang. Both did much more than myself.

❝ If I want to design an injection site study to compare the relative bioavailability at 3 different injection site, say T1, T2 vs R, in either crossover design or parallel design, is it correct to use the R code below:

In principle yes but as already mentioned by Divyen, theta0 = 1 should not be used.

❝ I also saw some posts suggest doing "two at a time" test, which will use the 2x2 design as follows (which gave essentially the same sample size as the 3x6x3 design above since I need to round up to 6X, so 40 becomes 42). Is this thought process correct?

❝ Parallel design (3 arms, assuming true theta=1, pooled CV=0.4). R results indicate I need 132 total subjects (44 subjects per arm), not considering drop out etc. Is it correct, or the 132 is for 2 arms (66 per arm) and I actually need 198 total subjects?

Yes.

Dif-tor heh smusma 🖖🏼 Довге життя Україна!
Helmut Schütz

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