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Statistics — SCE Medical Oncology MCQ

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HardClinical Trials & StatisticsStatisticsSCE Medical Oncology

An oncology trial reports median PFS of 12 versus 6 months and a Cox hazard ratio of 0.50. Why is the claim “patients have 50% longer PFS” not justified by the hazard ratio?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — It compares instantaneous event rates under the model, not survival-time gain or absolute event-free probability

Explanation lettering: C = shown as B · D = shown as C · E = shown as D · B = shown as E

A is correct. A hazard ratio of 0.50 describes the relative hazard of progression or death over time under the fitted model, commonly with a proportional-hazards interpretation. It is not an absolute probability, an individual time gain or proof that survival time increases by 50%. B turns a group median into a guaranteed individual benefit. C confuses hazard with the survival function. D invents a requirement for Kaplan-Meier curves to fall to zero. E cannot derive a number needed to treat without absolute risks at a specified time. Median difference, landmark survival, restricted mean survival and toxicity help communicate magnitude alongside the hazard ratio.

Reference: Hazard ratios in cancer clinical trials: a primer: https://pmc.ncbi.nlm.nih.gov/articles/PMC7457144/