I have tried to answer your questions in below.
1-what are the issues that might rise when overpower our primary endpoint in
CT.
- Number one is ethical issue and hence regulatory bodies may not give the pre-approval to conduct the trial. Another point is that unnecessarily the cost of trial will be increased.
2- could we perform an interim analysis to increase our sample size in CT.
- Yes it can be done and people do. Cui, Hung and Wang (1991) suggested a novel method to increase sample size.
3- I want to perform a cross over trial. how can calculate the sampel size?
- I don't think that sample size calculation formula will change. Only thing you need to keep in mind that estimate of variance in Cross-over trial is less than that of parallel trial. If you have no idea how much it is less then you can consider just half of the variance estimate from parallel trial.
4- why we attend to perform non-inferiority trial rather than equivalence.
- It depends on the trial objective. Requirement of sample size for equivalence study is higher than the non-inferiority trial. In non-inferiority trial we try to prove that the test drug is not inferior than the standard one; we don't care wether the test drug is better than the standard one or not. On the contrary, in equivalence trial we need to make sure that drug is neither better nor the inferior than the standard drug.
Best regards,
--------------
Madan Gopal Kundu
Biostatistician, Ranbaxy Labs. Ltd.
Gurgaon, Haryana
India
Web: http://www.freewebs.com/madanstata
mobile: 91-9868788406
e-mail: [log in to unmask]
--- On Fri, 15/8/08, Abouihia Abdallah <[log in to unmask]> wrote:
From: Abouihia Abdallah <[log in to unmask]>
Subject: STAT question
To: [log in to unmask]
Date: Friday, 15 August, 2008, 8:12 PM
Dear Stasticians,
I have the following questions:
1-what are the issues that might rise when overpower our primary endpoint in
CT.
2- could we perform an interim analysis to increase our sample size in CT.
3- I want to perform a cross over trial. how can calculate the sampel size?
4- why we attend to perform non-inferiority trial rather than equivalence.
Many thanks in advance for your reponse.
Abdallah
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