Epidemiology: interpreting a hazard ratio: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Epidemiology: interpreting a hazard ratio

Sample item

In a randomised trial of two cancer regimens analysed with Cox proportional hazards regression, the hazard ratio for death with the new regimen compared with standard treatment is 0.70 (95% CI 0.55 to 0.88). Which interpretation is correct?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. At any time in follow-up, the instantaneous risk of death is about 30% lower with the new regimen

A hazard ratio compares the instantaneous event rates of two groups over time, assuming it is constant. A value of 0.70 means a 30% lower hazard at any moment, and since the interval excludes 1 the difference is statistically significant. It is not the same as a difference in proportions, median survival or odds.

Option by option

  • A. The proportion alive at the end of the study is 30 percentage points higher with the new regimen

    A hazard ratio is a relative rate and does not give an absolute difference in proportions surviving.

  • B. At any time in follow-up, the instantaneous risk of death is about 30% lower with the new regimen (correct)

    Correct. The hazard ratio expresses a relative reduction in the event rate at any point in follow-up.

  • C. The odds of dying within one year are 0.7 times those with standard treatment

    Odds of death at a fixed time would be estimated by an odds ratio, for example from logistic regression.

  • D. Median survival is 30% longer with the new regimen

    A hazard ratio does not directly give a percentage change in median survival time.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this PSM question

What is the answer to this PSM question?

The best answer is B, At any time in follow-up, the instantaneous risk of death is about 30% lower with the new regimen. A hazard ratio compares the instantaneous event rates of two groups over time, assuming it is constant.

Why is "The proportion alive at the end of the study is 30 percentage points…" not the answer?

A hazard ratio is a relative rate and does not give an absolute difference in proportions surviving.

Why is "The odds of dying within one year are 0.7 times those with standard t…" not the answer?

Odds of death at a fixed time would be estimated by an odds ratio, for example from logistic regression.

Why is "Median survival is 30% longer with the new regimen" not the answer?

A hazard ratio does not directly give a percentage change in median survival time.

What concept does this question test?

It tests Epidemiology: interpreting a hazard ratio in PSM. A value of 0.70 means a 30% lower hazard at any moment, and since the interval excludes 1 the difference is statistically significant. It is not the same as a difference in proportions, median survival or odds.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Epidemiology: interpreting a hazard ratio?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.