A non-inferiority study is a specific type of clinical trial designed to demonstrate that a new treatment is not unacceptably worse than an already established standard therapy (active control). Unlike a superiority study, which aims to prove that the new treatment is better, a non-inferiority study focuses on demonstrating equivalence within a predefined, clinically acceptable margin (the non-inferiority margin, Δ).
Such studies are useful when the new treatment offers other advantages, such as better tolerability, easier administration, or lower costs, and superiority in efficacy is not expected. The design and statistical analysis of non-inferiority studies are complex. The choice of the margin must be well-justified and accepted by regulatory authorities. For CRO biostatisticians, planning these studies requires particular care to ensure that the results are interpretable and meet regulatory requirements.