Epidemiology: attributable risk percent: 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: attributable risk percent

Sample item

In a cohort study, the relative risk of lung cancer among smokers compared with non-smokers is 5. What proportion of lung cancer among the smokers can be attributed to smoking?

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

The answer and the reasoning

B. 80%

The attributable risk percent (etiological fraction in the exposed) equals (RR - 1) / RR x 100. With RR = 5 this is 4 / 5 = 80%. It tells how much of the disease in exposed persons would be eliminated if the exposure were removed, assuming a causal relationship.

Option by option

  • A. 20%

    This is 1 / RR, the proportion of disease in the exposed that would have occurred anyway.

  • B. 80% (correct)

    Correct. (5 - 1) / 5 = 0.8, so 80% of cancers in smokers are attributable to smoking.

  • C. 25%

    This is 1 / (RR - 1), which is not a meaningful epidemiological measure here.

  • D. 400%

    This is RR - 1 written as a percentage; the attributable fraction cannot exceed 100%.

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.

More PSM questions

Questions about this PSM question

What is the answer to this PSM question?

The best answer is B, 80%. The attributable risk percent (etiological fraction in the exposed) equals (RR - 1) / RR x 100.

Why is "20%" not the answer?

This is 1 / RR, the proportion of disease in the exposed that would have occurred anyway.

Why is "25%" not the answer?

This is 1 / (RR - 1), which is not a meaningful epidemiological measure here.

Why is "400%" not the answer?

This is RR - 1 written as a percentage; the attributable fraction cannot exceed 100%.

What concept does this question test?

It tests Epidemiology: attributable risk percent in PSM. With RR = 5 this is 4 / 5 = 80%. It tells how much of the disease in exposed persons would be eliminated if the exposure were removed, assuming a causal relationship.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: attributable risk percent?

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.