A non-inferiority trial asks whether a new approach is not worse than the standard by more than a set margin. The conclusion is only as good as that margin. In SOLARIO the margin was 10 percentage points in treatment failure — the upper limit of the confidence interval (3.0 points) sat well inside it, which is reassuring. A trial whose interval reaches right up to its margin supports a much weaker claim, and a generous margin can make almost anything non-inferior.
- Find the prespecified margin and ask whether you would accept a difference that large.
- Check where the upper end of the confidence interval falls relative to the margin.
- Look for a per-protocol analysis agreeing with the intention-to-treat one — in non-inferiority trials, dropouts can hide a difference.
- Non-inferior on efficacy plus clearly better on harms is the strongest case for switching.
Why it matters
Most treatment-shortening trials are non-inferiority designs, and the margin decides how much risk you are accepting.
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