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
twosamplemeans test = EQUIV_diff
meandiff = 0
stddev = 25
npergroup = .
lower = -10
upper = 10
alpha = 0.025 0.05
power = 0.8;
... 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?
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.
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'.