Noninferiority Trials

Some new treatments proffer not an improved therapeutic effect in comparison to a standard treatment but less toxicity, lower expense, or, as in the study of time-expanded HPV vaccine schedules, easier administration. Studies to assess these new treatments are not designed to determine whether they are better than the standard treatment, but rather whether they result in the same effect.¹ Such studies are called “noninferiority” or “equivalence” trials. An equivalence trial seeks to determine whether a treatment is therapeutically similar to another.² Typically, the authors define, a priori, a difference between the two treatment groups (Δ) that is considered to be clinically relevant. Equivalence is thus defined as a difference in the treatment effect less than Δ in either direction. A noninferiority trial is very similar, except that it seeks to determine whether …