# st: RE: equivalence trial power calculation

 From "Moran, John (NWAHS)" <[email protected]> To "'[email protected]'" <[email protected]> Subject st: RE: equivalence trial power calculation Date Wed, 8 Oct 2003 09:35:09 +0930

```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,

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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