What does "Non-Inferiority Margin" mean?

Definition of Non-Inferiority Margin in the context of A/B testing (online controlled experiments).

What is a Non-Inferiority Margin?

A non-inferiority margin is such a difference m that we would be happy implementing a tested treatment if we are to be able to rule out outcomes below -m (negative and smaller in magnitude than m) with our desired significance threshold.

The non-inferiority margin should not be chosen lightly: it should be informed by as objective criteria as possible and it should be communicated to all stakeholders before the A/B test begins.

Like this glossary entry? For an in-depth and comprehensive reading on A/B testing stats, check out the book "Statistical Methods in Online A/B Testing" by the author of this glossary, Georgi Georgiev.

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