"Just as good" treatment effects are established in non-inferiority trials
The margin of non-inferiority needs to be stipulated in an a priori fashion. The cut-point and margin both need to be identified a priori. After observations are collected, the means and standard deviations (continuous outcome) or the odds ratios with 95% confidence intervals (categorical outcome) are compared to the cut-point or population value and the margin of non-inferiority.
When to use non-inferiority trials
1. It is not ethically possible to conduct a placebo-controlled trial.
2. The experimental treatment is not expected to be better than the control treatment on a primary efficacy endpoint, but is better on secondary endpoints or is safer.
3. The experimental treatment is not expected to be better than the control treatment on a primary efficacy endpoint, but is cheaper to produce or easier to administer.
4. The experimental treatment is not expected to be better than the control treatment on a primary efficacy endpoint, but compliance to the treatment will be better.
Interpreting non-inferiority trial outcomes
So, if the upper limit of the confidence interval does NOT cross over the upper limit of the margin of equivalence, you CAN assume non-inferiority and your p-value will be LESS THAN .025.
However, if the upper limit of the confidence interval crosses over the upper limit of the margin of equivalence, you CANNOT assume non-inferiority and your p-value will be MORE THAN .025.
Click on the Non-Inferiority Trial Calculator button to download a free calculator for non-inferiority trials.
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