Epidemiology: population 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: population attributable risk percent

Sample item

In a community, 20% of adults are exposed to indoor biomass smoke, and the relative risk of chronic bronchitis in exposed adults is 4. What is the population attributable risk percent?

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

The answer and the reasoning

A. 37.5%

Population attributable risk percent = Pe (RR - 1) / [1 + Pe (RR - 1)] x 100, where Pe is the proportion of the population exposed. Here Pe (RR - 1) = 0.2 x 3 = 0.6, so the result is 0.6 / 1.6 = 37.5%. It tells the planner how much of the disease burden in the whole community could be prevented by removing the exposure.

Option by option

  • A. 37.5% (correct)

    Correct. 0.6 divided by 1.6 gives 37.5% of bronchitis in the community attributable to smoke exposure.

  • B. 20%

    This is simply the prevalence of exposure and is not a measure of attributable risk.

  • C. 60%

    This is only the numerator, 0.6, without dividing by 1 plus that term.

  • D. 75%

    This is the attributable risk percent in the exposed ((4 - 1) / 4), which ignores how common the exposure is.

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 A, 37.5%. Population attributable risk percent = Pe (RR - 1) / [1 + Pe (RR - 1)] x 100, where Pe is the proportion of the population exposed.

Why is "20%" not the answer?

This is simply the prevalence of exposure and is not a measure of attributable risk.

Why is "60%" not the answer?

This is only the numerator, 0.6, without dividing by 1 plus that term.

Why is "75%" not the answer?

This is the attributable risk percent in the exposed ((4 - 1) / 4), which ignores how common the exposure is.

What concept does this question test?

It tests Epidemiology: population attributable risk percent in PSM. Here Pe (RR - 1) = 0.2 x 3 = 0.6, so the result is 0.6 / 1.6 = 37.5%. It tells the planner how much of the disease burden in the whole community could be prevented by removing the exposure.

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: population 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.