A non-inferiority study is designed to test whether one treatment is not worse than another.

Non-inferiority studies are common in drug trials. They are intended to demonstrate that the effect of a new treatment is not worse than that of a reference treatment by more than a specified margin. Contrary to classical statistical hypothesis testing, non-inferiority and equivalence trials amount to an inversion of the typical Neyman-Pearson hypothesis testing approach, in that the researcher is trying to prove a type of null hypothesis. Because a finding of equivalence would technically also be considered a 'success', and because it is impossible to prove that an estimated parameter is equal to any point value, there remains uncertainty that the treatment is actually worse by an amount too small to be detected. This fact implies there are additional complexities in non-inferiority studies relative to superiority trials.

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