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Confidence interval interpretation — FRCA Primary MCQ

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HardStatistics and EBMConfidence interval interpretationFRCA Primary

An equivalence trial prespecifies a margin of −5 to +5 mmHg for the difference between two induction agents. The appropriate confidence interval for the observed difference is −2 to +4 mmHg. What is the correct interpretation?

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Correct answer: E — Equivalence is supported because the interval remains within both margins

The best answer is “Equivalence is supported because the interval remains within both margins”. Equivalence requires the complete confidence interval for the treatment difference to fall inside both prespecified limits. The interval from −2 to +4 mmHg lies wholly within −5 to +5 mmHg, so equivalence is supported. Crossing zero is compatible with equivalence and does not invalidate the conclusion.

Reference: Ranganathan et al., Equivalence trials: https://pmc.ncbi.nlm.nih.gov/articles/PMC9106130/