A useful formula (reference 1) is:
N (sample size per group) =2p(1-p)(z_1-alpha + z_1-beta)^2 / delta^2
Where p = event rate (assumed to be the same in each group), and delta is
the maximal acceptable difference in event rates.
For continuous outcomes: N = 2sigma^2(z_1-alpha + z_1-beta)^2 / delta^2
(delta is the minimum difference between treatment groups that is
"important" to detect; _not_, as for a superiority trial, the maximally
acceptable difference).
A few references:
(1) Kim MY, Buyon JP, Petri M, Skovron ML, Shore RE (1999)
Equivalence trials in SLE research: issues to consider. Lupus 8:620-626
(2) Makuch R, Simon R (1978) Sample size requirements for
evaluating a conservative therapy. Cancer Treatment Reports 62:1037-40
(3) Blackwelder WC (1982) "Proving the null hypothesis" in
clinical trials. Contol Clin Trials 3:345-53
(4) Lin SC (1995) Sample size for therapeutic equivalence based
on confidence interval. Drug Inf J 29:45-50
(5) Jones B, Jarvis P, Lewis JA, Ebbutt AF (1996) Trials to
assess equivalence: the importance of rigorous methods. BMJ 313:36-39
[email protected]
-----Original Message-----
From: Jannik Helweg-Larsen [mailto:[email protected]]
Sent: Wednesday, October 08, 2003 6:08 AM
To: [email protected]
Subject: st: equivalence trial power calculation
Dear list
Using Stata 8.1
I'm unsure on how to calculate the required sample for the following trial,
been searching by findit for equivalence ado's without finding my answer:
We are planning to do a 2 year equivalence trial.The current standard of
treatment has a 2 year failure rate of 7%: In our trial of a new drug, the
treatments will be considered equivalent if the 95% confidence interval are
within the bound of -12% to 12%, which we believe is the the largest
difference that would be considered clinically acceptable.
any suggestions?
Jannik Helweg-Larsen
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