Programming the statistical procedures from SAS

Proc Power: How to specify the type I error level when testing for equivalence

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New Contributor
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Proc Power: How to specify the type I error level when testing for equivalence

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?

Respected Advisor
Posts: 2,655

Re: Proc Power: How to specify the type I error level when testing for equivalence

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

New Contributor
Posts: 3

Re: Proc Power: How to specify the type I error level when testing for equivalence

Steve, you're on the safe side Smiley Wink

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

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