The hypotheses for an equivalence test are

where and are the lower and upper bounds specified in the TOST option in the PROC TTEST statement, and is the analysis criterion (mean, mean ratio, or mean difference, depending on the analysis). Following the two one-sided tests (TOST) procedure of Schuirmann (1987), the equivalence test is conducted by performing two separate tests:

and

The overall p-value is the larger of the two p-values of those tests.

Rejection of in favor of at significance level occurs if and only if the 100(1 – 2 )% confidence interval for is contained completely within . So, the 100(1 – 2 )% confidence interval for is displayed in addition to the usual 100(1 – )% interval.

For further discussion of equivalence testing for the designs supported in the TTEST procedure, see Phillips (1990); Diletti, Hauschke, and Steinijans (1991); Hauschke et al. (1999).