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05-24-2013 10:40 AM

I am planning the sample size for an equivalence trial with two parallel groups and a metric clinical outcome (comparison of mean values). The type I error level of the (two-sided) equivalence problem will be alpha=0.05, corresponding to the inclusion of the two-sided 95% conficence interval for the point estimate between the lower and the upper bound of the equivalence range. The null hypothesis will be tested by performing two one-sided tests against the lower and the upper bound, each with a one-sided type I error level of alpha/2 = 0.025.

When I calcuilate the sample size using Proc Power as in

**proc** **power**;

twosamplemeans test = EQUIV_diff

meandiff = **0**

stddev = **25**

npergroup = **.**

lower = -**10**

upper = **10**

alpha = **0.025** **0.05**

power = **0.8**;

**run**;

... do the values that I specify for alpha correspond to the two-sided case (i.e., to the procedure as a whole), or to the one-sided error level of each of the two one-sided tests? Which value for alpha will be appropriate for the test problem described above?

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05-30-2013 03:03 PM

Good question. I have always treated them as corresponding to the two-sided case. If this is incorrect, I hope someone can let us know.

Steve Denham

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05-31-2013 03:21 AM

Steve, you're on the safe side

Since there have been no responses for days (from which I have concluded that the topic is either not of interes, self-evident, or nobody really knows), and as I do not have access to SAS myself, I have cintacted their support, and they have oinformed me that the two-sided case is the program default. You can override this by specifying 'sides=1'.

Andreas