[Methodology for superiority versus equivalence and non-inferior clinical studies. A practical review]

Physicians should always remember that a negative result in a superiority trial never would prove that the therapies under research are equivalent; more often, there may be a risk of type 2 (false negative) error. Equivalence and not inferiority studies demand high standards to provide reliable results. Physicians should take into account above all that the equivalence margins tend to be too large to be clinically significant and that the claim of equivalence can be misleading if a study has not been conducted at a sufficiently high level. In addition, physicians must be a bit skeptical of judgments that do not include the basic requirements of information, including the definition and justification of the equivalence margin, the calculation of the size of the sample bearing in mind this margin, the presentation of both analysis (intention-to-treat and by protocol), and provide confidence intervals for the results. Equivalence and inferiority studies are not indicated in certain areas. If one follows the required strict adherence to the specific methodology, such studies can provide new and important knowledge.