Equivalence Test (TOST — Two One-Sided Tests)

The equivalence test using the Two One-Sided Tests (TOST) procedure is a parametric hypothesis test designed to demonstrate that the difference between two group means falls within a pre-specified equivalence region ±Δ. Introduced by Schuirmann (1987) in the context of pharmaceutical bioequivalence, TOST reverses the logic of classical null-hypothesis testing: instead of trying to detect a difference, it provides positive evidence of similarity.