  A bioequivalence study is a type of clinical trial designed to compare the
biological equivalence of two different formulations of a drug. Such studies
are typically conducted in controlled clinical settings with human subjects,
who are randomly assigned to receive two formulations. The two formulations are
then compared with respect to their pharmacokinetic profiles, which encompass
the absorption, distribution, metabolism, and elimination of the drug. Under
the guidance from Food and Drug Administration (FDA), for a size-$\alpha$
bioequivalence test, the standard approach is to construct a $100(1-2\alpha)\%$
confidence interval and verify if the confidence interval falls with the
critical region. In this work, we clarify that $100(1-2\alpha)\%$ confidence
interval approach for bioequivalence testing yields a size-$\alpha$ test only
when the two one-sided tests in TOST are ``equal-tailed''. Furthermore, a
$100(1-\alpha)\%$ confidence interval approach is also discussed in the
bioequivalence study.
