Biostatistics: 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 · Biostatistics

Sample item

In a cohort study, 20 of 100 exposed persons and 10 of 200 unexposed persons develop the disease. What is the relative risk?

A15B2C0.25D4

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

The answer and the reasoning

D. 4

Risk in the exposed is 20/100, or 0.20, and risk in the unexposed is 10/200, or 0.05. Relative risk is the ratio of the two, 0.20 divided by 0.05, which is 4.

Option by option

A. 15
A value of 15 corresponds to the difference in risk expressed per 100 persons, which is attributable risk and not a ratio.
B. 2
A value of 2 results from comparing the raw case counts (20 to 10) without adjusting for group sizes.
C. 0.25
A value of 0.25 results from inverting the ratio, dividing the unexposed risk by the exposed risk.
D. 4 (correct)
Correct. 0.20 divided by 0.05 gives a relative risk of 4.

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.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is D, 4. Risk in the exposed is 20/100, or 0.

Why is "15" not the answer?

A value of 15 corresponds to the difference in risk expressed per 100 persons, which is attributable risk and not a ratio.

Why is "2" not the answer?

A value of 2 results from comparing the raw case counts (20 to 10) without adjusting for group sizes.

Why is "0.25" not the answer?

A value of 0.25 results from inverting the ratio, dividing the unexposed risk by the exposed risk.

What concept does this question test?

It tests Biostatistics in PSM. 20, and risk in the unexposed is 10/200, or 0.05. Relative risk is the ratio of the two, 0.20 divided by 0.05, which is 4.

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 Biostatistics?

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.