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Dear All,
Can we calculate the sample size for two way crossover study on the
basis of Intra-subject CV obtained from replicate 4 period crossover
study?
Is there any proportionate formula for computing the sample size from
2-way to 4-way and vice versa? If not, will there any impact on
statistical outcome, if we do the study with direct calculation?
I would be thankful to you, if you will provide me some references.
Thanks
Prakash Patel
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The following message was posted to: PharmPK
Yes, you can. The IntraCV from a replicate is a great estimate and can
certainly be used to calculate sample size for a 2-way.
There is a proportionate from going to two-way to four-way and vice
versa. Divide the sample size estimate in a 2-way by 2 to get the
sample size for a 4-period replicate. To go from a 4-period replicate
to a 2-way, multiply by 2. Please note that a 4-way is not the same
thing as a 4-period replicate, a 4-way has 4 different treatments.
My favourite sample size reference:
Julious, SA. Statist. Med. 2004; 23:1921-1986
Hope this helps,
-Dave
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