Epidemiology: 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

Sample item

In a cohort study the incidence of a disease is 30 per 1000 in the exposed and 10 per 1000 in the unexposed. What is the attributable risk among the exposed?

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

The answer and the reasoning

A. 20 per 1000

Attributable risk is the difference between incidence in the exposed and the unexposed, here 30 minus 10 per 1000. It shows the excess disease due to exposure, while the ratio of 3 is the relative risk.

Option by option

  • A. 20 per 1000 (correct)

    The risk difference of 30 minus 10 gives 20 per 1000.

  • B. 10 per 1000

    Ten per 1000 is the incidence in the unexposed, the background risk.

  • C. 3 per 1000

    Three is the relative risk, a ratio, not a difference.

  • D. 40 per 1000

    Forty adds the two incidences, which has no epidemiological meaning.

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, 20 per 1000. Attributable risk is the difference between incidence in the exposed and the unexposed, here 30 minus 10 per 1000.

Why is "10 per 1000" not the answer?

Ten per 1000 is the incidence in the unexposed, the background risk.

Why is "3 per 1000" not the answer?

Three is the relative risk, a ratio, not a difference.

Why is "40 per 1000" not the answer?

Forty adds the two incidences, which has no epidemiological meaning.

What concept does this question test?

It tests Epidemiology in PSM. It shows the excess disease due to exposure, while the ratio of 3 is the relative risk.

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?

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.