Non-inferiority trials: No better? No worse? No change? No pain?

With improvements in care over time it becomes harder to improve clinical outcomes in those conditions where cure rates are high. The focus of research can thus turn to the so-called non-inferiority trial: where the main aim is not to improve clinical outcome, but instead to provide evidence of a lack of difference, whilst other issues, such as cost or toxicity, are improved. The interpretation of such trials is not always straightforward. The burden of proof is reversed compared to a traditional superiority trial, and this means that many of the statistical safeguards, such as significance and intention-to-treat, which act as restraints from an overhasty adoption of a new therapy, may actually work in the opposite fashion. The issues regarding non-inferiority and equivalence trials are considered, and their interpretation discussed.