Conflict of interest: none declared. Financial support: none declared.
The aim of non-inferiority trials is to show that a new treatment is not less effective than standard treatment, in other words ‘non-inferior’.
The non-inferiority margin should be determined before a study commences. This margin determines the maximal magnitude of difference in effectiveness permissible if it is to be concluded that a new treatment is not less effective than the standard treatment.
There is usually a good reason for a non-inferiority design. For example, because the new treatment is easier to use, provides better cost-effectiveness or has fewer side effects.
The reader of a non-inferiority trial should consider a number of aspects critically: (a) the reason for use of this study design, (b) the assumed benefit of the new treatment, (c) the rationale for the choice of non-inferiority margin and (d) the choice of the standard therapy with which the new treatment is compared.