Abstract
Equivalent testing has been strongly recommended for demonstrating the comparability of treatment effects in a wide variety of research fields including medical studies. Although the essential properties of the favorable two one-sided tests of equivalence have been addressed in the literature, the associated power and sample size calculations were illustrated mainly for selecting the most appropriate approximate method. Moreover, conventional power analysis does not consider the allocation restrictions and cost issues of different sample size choices. To extend the practical usefulness of the two one-sided tests procedure, this article describes exact approaches to sample size determinations under various allocation and cost considerations. Because the presented features are not generally available in common software packages, both R and SAS computer codes are presented to implement the suggested power and sample size computations for planning equivalence studies. The exact power function of the TOST procedure is employed to compute optimal sample sizes under four design schemes allowing for different allocation and cost concerns. The proposed power and sample size methodology should be useful for medical sciences to plan equivalence studies.
Highlights
Equivalence tests have been widely adopted for demonstrating the bioequivalence between two drug formulations in biopharmaceutical studies
With the exact power function of the two one-sided tests (TOST) procedure, this study examines research designs with the allocating and budgetary constraints
Detailed discussions and related results of the Minnesota Multiphasic Personality Inventory (MMPI) differences between alcoholics and drug abusers can be found in Cannon, Bell, and Fowler [31]
Summary
Equivalence tests have been widely adopted for demonstrating the bioequivalence between two drug formulations in biopharmaceutical studies. The notion of equivalence between treatment effects is relevant and potentially useful in other of research fields such as medical sciences. It is not the uniformly most powerful test and more powerful tests exist, the two one-sided tests (TOST) procedure proposed by Schuirmann [1] and Westlake [2] is the most common method for equivalence assessment under a two-group parallel design. Rogers et al [8] emphasized that the traditional test and the equivalence test are not mutually exclusive. If both test procedures are performed, it is possible that both will be rejected, that neither will be rejected, or that one will be PLOS ONE | DOI:10.1371/journal.pone.0162093 September 6, 2016
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