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 trial, the event rate is 20 percent in the control group and 15 percent in the treated group. What is the number needed to treat?

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

The answer and the reasoning

D. 20

The absolute risk reduction is 20 percent minus 15 percent, which is 5 percent or 0.05. The number needed to treat is the reciprocal of the absolute risk reduction, 1 divided by 0.05, which is 20.

Option by option

  • A. 4

    4 results from dividing the 20 percent by the 5 percent difference.

  • B. 10

    10 has no basis in this calculation.

  • C. 5

    5 is the absolute risk reduction in percentage points, not its reciprocal.

  • D. 20 (correct)

    Correct. NNT is 1 divided by the absolute risk reduction.

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 D, 20. The absolute risk reduction is 20 percent minus 15 percent, which is 5 percent or 0.

Why is "4" not the answer?

4 results from dividing the 20 percent by the 5 percent difference.

Why is "10" not the answer?

10 has no basis in this calculation.

Why is "5" not the answer?

5 is the absolute risk reduction in percentage points, not its reciprocal.

What concept does this question test?

It tests Biostatistics in PSM. 05. The number needed to treat is the reciprocal of the absolute risk reduction, 1 divided by 0.05, which is 20.

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 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.